chore(docs): adding quick reference to oracles, guide and explainer to follow

[signorecello]

Description

Adds almost a "dummy" page on Oracles to the reference section (here called "concepts" due to the almost inevitable mix between explanations and language reference)

Problem*

Closes #3971

Summary*

• Adds an "oracles" page to the concepts section simply explaining how to use the flag and mentioning the RPC server. Intentionally, there is no info on how to write the RPC server and how to pass it to the oracle function, as that falls outside of the scope of the language, and thus should be part of a how-to guide
• Updates sibebar item order and adds it to Traits. This is mostly unecessary but for the time being we can totally manage them and profit from controlling sidebar ordering

Additional Context

We can almost consider this 1/3 of the work, so I'm glad making it a draft now and add it to a bigger PR with the guide/explainer. Just wanted to close #3971 for the time being

[github-actions]

🚀 Deployed on https://659bd71a02b53d41d597ff52--noir-docs.netlify.app

[Savio-Sou]

part of a how-to guide
That's going into the "How To Guides" section of the docs right?

In that case would prefer closing #3971 when we have the guide ready for merging instead.

(Feel free to update the original Issue for better alignment with the diátaxis framework if need to.)

[TomAFrench]

tbh, this seems to give just enough information to entice extra questions on this topic without allowing users to actually use these. This is probably counterproductive in terms of saving time spent helping people use oracles

[signorecello]

Agreed! Making it a draft and reusing this branch for the rest of it

[signorecello]

Superseeded by #4002