Model Doc updates

[vEpiphyte]

• Move all structured model entries from changelog.rst to their own files in the user guide section.
• Update tool documentation to use aha:// URLs
• Add v2.177.0 model reference file.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.29%. Comparing base (b7da795) to head (382e5c1).

Files	Patch %	Lines
synapse/tools/changelog.py	50.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3839 +/- ## ========================================== - Coverage 96.36% 96.29% -0.08% ========================================== Files 242 242 Lines 53770 53771 +1 ========================================== - Hits 51815 51777 -38 - Misses 1955 1994 +39 ``` | [Flag](https://app.codecov.io/gh/vertexproject/synapse/pull/3839/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | Coverage Δ | | |---|---|---| | [linux](https://app.codecov.io/gh/vertexproject/synapse/pull/3839/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | `96.29% <50.00%> (-0.01%)` | :arrow_down: | | [linux_replay](https://app.codecov.io/gh/vertexproject/synapse/pull/3839/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | `?` | | 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=vertexproject#carryforward-flags-in-the-pull-request-comment) to find out more.

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