Improve UX of `Configuration`

[LVala]

With this PR:

• Users can configure whether they want to use features like Sender/Receiver Reports, TWCC, RTX, etc.
• adds necessary RTP header extensions, RTCP feedbacks, and RTX codecs by default depending on features enabled
• in general, created SDPs correspond to the config more closely

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 91.38577% with 23 lines in your changes missing coverage. Please review.

Project coverage is 87.01%. Comparing base (2fb532b) to head (04f0ee7).

:exclamation: Current head 04f0ee7 differs from pull request most recent head 799f237

Please upload reports for the commit 799f237 to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #120 +/- ## ========================================== - Coverage 88.01% 87.01% -1.00% ========================================== Files 34 34 Lines 1727 1802 +75 ========================================== + Hits 1520 1568 +48 - Misses 207 234 +27 ``` | [Files](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc) | Coverage Δ | | |---|---|---| | [lib/ex\_webrtc/media/ogg/page.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?src=pr&el=tree&filepath=lib%2Fex_webrtc%2Fmedia%2Fogg%2Fpage.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9tZWRpYS9vZ2cvcGFnZS5leA==) | `97.87% <ø> (ø)` | | | [lib/ex\_webrtc/rtp\_receiver/simulcast\_demuxer.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?src=pr&el=tree&filepath=lib%2Fex_webrtc%2Frtp_receiver%2Fsimulcast_demuxer.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9ydHBfcmVjZWl2ZXIvc2ltdWxjYXN0X2RlbXV4ZXIuZXg=) | `96.15% <ø> (ø)` | | | [lib/ex\_webrtc/rtp\_sender.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?src=pr&el=tree&filepath=lib%2Fex_webrtc%2Frtp_sender.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9ydHBfc2VuZGVyLmV4) | `93.75% <100.00%> (+0.89%)` | :arrow_up: | | [lib/ex\_webrtc/rtp\_transceiver.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?src=pr&el=tree&filepath=lib%2Fex_webrtc%2Frtp_transceiver.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9ydHBfdHJhbnNjZWl2ZXIuZXg=) | `91.35% <100.00%> (-1.33%)` | :arrow_down: | | [lib/ex\_webrtc/sdp\_utils.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?src=pr&el=tree&filepath=lib%2Fex_webrtc%2Fsdp_utils.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9zZHBfdXRpbHMuZXg=) | `92.41% <ø> (ø)` | | | [lib/ex\_webrtc/rtp\_receiver.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?src=pr&el=tree&filepath=lib%2Fex_webrtc%2Frtp_receiver.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9ydHBfcmVjZWl2ZXIuZXg=) | `71.01% <72.72%> (-7.68%)` | :arrow_down: | | [lib/ex\_webrtc/peer\_connection/configuration.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?src=pr&el=tree&filepath=lib%2Fex_webrtc%2Fpeer_connection%2Fconfiguration.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9wZWVyX2Nvbm5lY3Rpb24vY29uZmlndXJhdGlvbi5leA==) | `94.92% <96.29%> (+3.26%)` | :arrow_up: | | [lib/ex\_webrtc/peer\_connection.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?src=pr&el=tree&filepath=lib%2Fex_webrtc%2Fpeer_connection.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9wZWVyX2Nvbm5lY3Rpb24uZXg=) | `81.20% <81.01%> (-2.27%)` | :arrow_down: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc) ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?dropdown=coverage&src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). Last update [2fb532b...799f237](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/120?dropdown=coverage&src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc).