Changelog for v2.177.0, changelog tool updates

[vEpiphyte]

• Update changelog tool to add model saver, differ, and model awareness options to the output of the format functions.
• Add changelog for v2.177.0 release
• Start changelog tool tests
• Add reference model for v2.176.0

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 76.21832% with 122 lines in your changes missing coverage. Please review.

Project coverage is 96.29%. Comparing base (241e0ea) to head (cff5d21).

Files	Patch %	Lines
synapse/tools/changelog.py	76.21%	122 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3836 +/- ## ========================================== - Coverage 96.82% 96.29% -0.54% ========================================== Files 241 242 +1 Lines 53089 53770 +681 ========================================== + Hits 51403 51776 +373 - Misses 1686 1994 +308 ``` | [Flag](https://app.codecov.io/gh/vertexproject/synapse/pull/3836/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/3836/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | `96.29% <76.21%> (-0.47%)` | :arrow_down: | | [linux_replay](https://app.codecov.io/gh/vertexproject/synapse/pull/3836/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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