[feature] support configuring database caches

[NyaaaWhatsUpDoc]

Description

• adds CacheConfiguration{} options to main configuration struct, allowing setting via config file
• update config helpers generator to support nested structs
• add example cache config variables to config tests

Checklist

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.

[NyaaaWhatsUpDoc]

Only thing still remaining is to update example configuration file, and possibly update other areas of documentation? And tests clearly...

[NyaaaWhatsUpDoc]

In time I want to add intelligent default for cache sizes.

[NyaaaWhatsUpDoc]

This lays the groundwork for any changes (if we decide to make them) in #1244

[tsmethurst]

Nice one kim! this looks really good :)

We gotta remember when we cut a release including these changes to include a migration note about the config format changing to allow nesting.

Also, do you foresee any issues with the nesting? I mean, could it break if one provides a config that doesn't nest?

[NyaaaWhatsUpDoc]

Nice one kim! this looks really good :)

We gotta remember when we cut a release including these changes to include a migration note about the config format changing to allow nesting.

Also, do you foresee any issues with the nesting? I mean, could it break if one provides a config that doesn't nest?

for this specific PR there shouldn't be any breaking changes. the only nested values are new ones so shouldn't be an issue. for later PRs though -- I added a note about this in the issue #1244 :)

[tsmethurst]

Great :) Just the one comment. Feel free to merge this after you've addressed it!