Generalization for multi-game support

[FM-17]

• Rephrased embed text to be more general. If an unrecognized endpoint is provided, the posted embed will simply say "Official Server rates have been updated" rather than stating that ARK's rates have been updated, or specifying a game mode (smalltribes, classic, etc)
• Added a few ATLAS-specific rate nicknames to the RATES_NAMES dict.
• Updated docs to include --send-embed-on-startup

Note: I initially commited to main by accident, so I popped these changes into this branch and rolled back main to its last stable commit. In doing so, I believe I overshot it by one commit, therefore some of the systemd changes are also included in this commit. Probably not a big deal.

[codecov[bot]]

Codecov Report

Base: 92.83% // Head: 92.83% // No change to project coverage :thumbsup:

Coverage data is based on head (8576d8e) compared to base (592844d). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #68 +/- ## ======================================= Coverage 92.83% 92.83% ======================================= Files 10 10 Lines 405 405 ======================================= Hits 376 376 Misses 29 29 ``` | [Impacted Files](https://codecov.io/gh/FM-17/poglink/pull/68?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [poglink/models/rates.py](https://codecov.io/gh/FM-17/poglink/pull/68/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-cG9nbGluay9tb2RlbHMvcmF0ZXMucHk=) | `100.00% <ø> (ø)` | | | [poglink/cogs/rates.py](https://codecov.io/gh/FM-17/poglink/pull/68/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-cG9nbGluay9jb2dzL3JhdGVzLnB5) | `97.97% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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[github-actions[bot]]

:tada: This PR is included in version 0.9.0 :tada:

The release is available on:

• GitHub release
• v0.9.0

Your semantic-release bot :package::rocket: