[Documentation] Improve RelayMiner staking related documentation

[red-0ne]

Summary

Improve supplier staking config and relay miner config documentation w.r.t upstaking, PRC types and Supplier<->RelayMiner signing_keyname relationship.

Issue

The documentation was not clear enough as to

• Why upstaking is needed to update the Supplier provided services.
• Why it is not possible to have multiple Suppliers assigned to the same RelayMiner
• What is the purpose of having multiple RPCTypes per Service provided

Type of change

Select one or more:

• [ ] New feature, functionality or library
• [ ] Bug fix
• [ ] Code health or cleanup
• [x] Documentation
• [ ] Other (specify)

Testing

Documentation changes (only if making doc changes)

• [x] make docusaurus_start; only needed if you make doc changes

Sanity Checklist

• [x] I have tested my changes using the available tooling
• [ ] I have commented my code
• [ ] I have performed a self-review of my own code; both comments & source code
• [ ] I create and reference any new tickets, if applicable
• [ ] I have left TODOs throughout the codebase, if applicable