Replace Towncrier with GitHub releases + labels.

[pixlwave]

We weren't using Towncrier very well so this PR replaces it with the use of GitHub's generated release notes along with a configuration that will categorise each entry based upon one of the following labels being applied:

Labels added here: https://github.com/element-hq/element-x-ios/labels?q=pr-

These labels can be added after the PR is merged, so long as they're there before the release is made.

The second commit removes Towncrier. I made a second repo to figure the flow out, but not sure how to validate the changes on EX other than wait for the next release and tidy up anything that comes out of that.

[github-actions[bot]]

	Warnings
:warning:	Some of the commits are missing ticket numbers. Please consider squashing all commits that don't have a tracking number.

Generated by :no_entry_sign: Danger Swift against 3c6540e69e0e031793212f9fdd606a21d408bb36

[pixlwave]

Oh yeah, Stefan asked this. Let's try in the test repo.

[pixlwave]

LGTM but what happens if a pr has multiple labels? Would it appear under multiple categories?

This PR had 3 tags, and the first one (I assume from the release.yml ordering) got chosen.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.05%. Comparing base (567f22b) to head (c82691d).

:exclamation: Current head c82691d differs from pull request most recent head 3c6540e

Please upload reports for the commit 3c6540e to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #2966 +/- ## =========================================== + Coverage 77.98% 78.05% +0.06% =========================================== Files 693 693 Lines 54172 54172 =========================================== + Hits 42248 42283 +35 + Misses 11924 11889 -35 ``` | [Flag](https://app.codecov.io/gh/element-hq/element-x-ios/pull/2966/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=element-hq) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/element-hq/element-x-ios/pull/2966/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=element-hq) | `68.91% <ø> (+0.06%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=element-hq#carryforward-flags-in-the-pull-request-comment) to find out more.

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[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud