Rework limits config

[Dav1dde]

We can organize the Limits struct in the config better, instead of having a max_* field for every limit and item type, we can use a similar Limit { ... } structure as used in #6250

This is a breaking change, so will require some considerations.

[linear-code]

RELAY-272

[pierceroberts]

@Dav1dde I see there was a PR merged. Is there still clean up work for this issue? Thanks!

[Dav1dde]

Not immediately, there is potentially some stuff we could organize better but that's a bigger breaking change which requires some thought first.