Deprecate settings.yml, and document usage

[jotaen4tinypilot]

Resolves #1524.

The outcome of our discussion in the ticket was this:

• The SQlite DB (tinypilot.db) should be the default place for new settings, whereas the YAML file (settings.yml) should only be used in exceptional cases, and obviously for legacy reasons.
• We favor having a single storage solution over a dual approach, as that simplifies future decision-making, and eliminates potential migration burden between the two storage formats.
• The SQlite DB doesn’t easily allow programmatic access right now (in contrast to the YAML file), so we created this ticket for removing this hurdle.
• We will document the parameters in settings.yml separately.

This PR adds a comment in settings.py, marking its usage as quasi-deprecated. It also adds some historical context, references the SQlite DB as default storage, and lists sample exceptional cases.

I realized that we probably don’t need to add any documentation to the SQlite DB, since there is not really an alternative to it any longer. So by deprecating settings.yml, the SQlite DB is the only storage option anyway, and there shouldn’t be any ambiguity left. Contrary to my initial proposal, I also don’t think we should move settings.py up to the app package, as that might mistakenly promote its usage.

[jdeanwallace]

Automated comment from CodeApprove ➜

✔️ Approved

Nice explanation.

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👀 @jotaen4tinypilot it's your turn please take a look