Tidy up and document configuration options in v2

[tgodzik]

Metals 2.0.0 added a lot of new option, some of them are unused and most undocumented.

We should:

1. Remove any that are not used
2. Merge any that have the same semantics
3. Make sure that the options are ok in UserConfiguration or do we need to do something like with bugfix: Initialize definitionIndexStrategy when initializing #8352
4. Create a guide for users to make it easy for them to experiment.

[krrish175-byte]

Hi @tgodzik : Hope you are doing well!

Can I take upon this issue?

[tgodzik]

Hey, I think this one is something I need to do myself with care and see the current state of all what we have.