[Request]: Move, reorganize Scheduled maintenance docs

[cfe316]

Feature description

Presently there are two copies of the maintenance documentation.
docs/src/Model_Reference/maintenance_overview.md
Maintenance

and
docs/src/Model_Reference/Resources/maintenance.md
Scheduled maintenance for various resources

The two are slightly different at the end, with one having some function references and one giving some advice on how to add maintenance to a resource.

Motivation

Docs will be cleaner & make more sense.

Implementation strategy

The docs should be deduplicated. One page should be placed in Resources/Thermal, since it's not for various resources.

If desired the more technical bits could be placed in the developer docs section.

Additional context

I plan on also putting Fusion docs in the Resources / Thermal folder.