feat: Support Aptible deployments

[rolodato]

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Changes

This PR adds functionality to enable deploying to Aptible, which an Enterprise prospect is currently evaluating. They have been able to work around these changes by forking open-source Flagsmith and making similar changes (i.e. removing waitfordb instead of making it optional). They would however need the changes to be upstreamed to deploy the Flagsmith Enterprise image.

Add /healthcheck as a health check route

Exposes the same health check endpoint on /healthcheck in addition to /health. Aptible (surprisingly) does not allow configuring a custom health check route and forces it to be /healthcheck. Strict health checks also do not accept redirects as responses.

There are some alternatives to directly adding /healthcheck as an alias of /health:

1. Add an option to make the health check route configurable. This would require a more thorough documentation review and is potentially error prone. YAGNI also applies since we have never needed to customise the health check route at the API level (i.e. not using a proxy in front of it) until now.
2. Add an option to opt in to the /healthcheck route, using some sort of "Aptible mode". I don't see a downside to always aliasing /health so this seems like extra complexity for no benefit.
3. Add an option for additional configurable health check routes, i.e. in addition to /health. I believe YAGNI also applies here and we can add it later if needed.

Add SKIP_WAIT_FOR_DB environment variable

When Aptible is deploying an application, it first checks for successful health checks before it is added to the same network as an Aptible-hosted database. This means that trying to deploy Flagsmith to Aptible without these changes will always fail when health checks fail while waitfordb is hanging.

This PR adds an environment variable that skips waiting for the database before running migrations or starting the API.

It seemed to me that an environment variable is the least intrusive and Aptible-specific way we could support this - happy to consider different approaches and variable/parameter names.

How did you test this code?

Deployed Flagsmith to a trial Aptible account here using the steps described in the docs from this PR: https://app-76164.on-aptible.com/. I'll add a link in the docs to the actual Flagsmith release that contains these changes once ready.

Please describe.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 12, 2024 2:05pm

2 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
flagsmith-frontend-preview	⬜️ Ignored (Inspect)	Visit Preview		Aug 12, 2024 2:05pm
flagsmith-frontend-staging	⬜️ Ignored (Inspect)	Visit Preview		Aug 12, 2024 2:05pm

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-e2e:pr-4340	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api-test:pr-4340	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-4340	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-api:pr-4340	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-4340	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-4340	Finished ✅	Results ✅

[github-actions]

Uffizzi Preview deployment-54225 was deleted.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.84%. Comparing base (b32a6ca) to head (305de0c).
Report is 50 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4340      +/-   ##
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+ Coverage   96.77%   96.84%   +0.06%     
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  Files        1159     1166       +7     
  Lines       38069    38675     +606     
==========================================
+ Hits        36842    37453     +611     
+ Misses       1227     1222       -5     

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[rolodato]

Got feedback from the prospect that this is working for them. The only thing that I haven't got working yet on Aptible is the task processor. It is possible to run it but need to keep experimenting with different settings.

[matthewelwell]

Got feedback from the prospect that this is working for them. The only thing that I haven't got working yet on Aptible is the task processor. It is possible to run it but need to keep experimenting with different settings.

Should we mark this PR as draft until this is done then? Or merge this and submit another PR for the task processor?

[dabeeeenster]

I vote to merge and then additional PRs if there's a need