Add Stats Graph SVG Render View

[Andrew-Dickinson]

Adds an endpoint to render SVG files for the website to display, in the style of the current nycmesh.net/stats page

Also does a bit of refactoring and cleanup in meshweb, we should probably spread the views out into multiple files, and we don't need to use the DRF decorators for non-API views

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.24460% with 8 lines in your changes missing coverage. Please review.

Project coverage is 94.21%. Comparing base (1496dbd) to head (73fb4b0). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/meshweb/views/website_stats.py	93.54%	8 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #707 +/- ## ========================================== + Coverage 94.11% 94.21% +0.09% ========================================== Files 82 86 +4 Lines 3418 3542 +124 ========================================== + Hits 3217 3337 +120 - Misses 201 205 +4 ```

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[Andrew-Dickinson]

The new graphs aren't identical, but they're really close. The biggest thing that's missing is the little green % diff indicator. I don't think matplotlib can really draw that, but if anyone has tips I would appreciate them

[Andrew-Dickinson]

Okay changed it so that we just render the graph in MeshDB. All the header stuff will be done on the website side, but I needed an API in order to expose the total counts publicly (using our standard API for this is a security hazard as the token would need to be public). Having this little JSON API also has the advantage of making it trivial to convert to a frontend graphing framework in the future if desired