feat: Use proxy for contacting Flagsmith

[GuyGitzMagen]

This pull request includes changes to the src/edge_proxy module to add a proxy configuration for HTTP clients. The most important changes include modifying the AppSettings class to include a proxy setting and updating the HTTP client initialization to use this proxy setting.

Proxy Configuration Addition:

• src/edge_proxy/settings.py: Added an optional proxy attribute to the AppSettings class.

HTTP Client Initialization:

• src/edge_proxy/environments.py: Updated the httpx.AsyncClient initialization to include the proxy setting.
• src/edge_proxy/server.py: Modified the httpx.AsyncClient initialization to use the proxy setting from AppSettings.

[dabeeeenster]

This config needs adding to docs if/when it gets merged too.

[matthewelwell]

Hi @GuyGitzMagen , thanks very much for the contribution. This is great. I've added a couple of minor comments, but please let me know if you'd rather we implement the changes in house from this point.

[rolodato]

I've not tested this, but if I'm not mistaken you can just use the ALL_PROXY or HTTP_PROXY+HTTPS_PROXY environment variables for this: https://www.python-httpx.org/environment_variables/

[matthewelwell]

I've not tested this, but if I'm not mistaken you can just use the ALL_PROXY or HTTP_PROXY+HTTPS_PROXY environment variables for this: https://www.python-httpx.org/environment_variables/

Nice, thanks @rolodato. @GuyGitzMagen are you able to test that and confirm that it works for your use case? If so, we'll close this PR and update the documentation on our side.

[GuyGitzMagen]

Thanks, it's working!
However, I'm a bit concerned about being tightly coupled to edge-proxy's internal client implementation. Would it make sense to add a test case to ensure this functionality remains supported in future versions?

[rolodato]

I've created a PR to document this here: Flagsmith/flagsmith#4928

[rolodato]

This is now documented here: https://docs.flagsmith.com/deployment/hosting/locally-edge-proxy#environment-variables