Unify RBAC flow in a single module

[nitisht]

This commit combines all the RBAC specific code in a single
crate. This improves readability.

Also added more relevant comments

[github-actions]

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[nitisht]

I have read the CLA Document and I hereby sign the CLA

[nitisht]

recheck

[nitisht]

@trueleo PTAL

[trueleo]

@nitisht Looks all good to me but one small thing is that we should keep src/rbac.rs on top level instead of moving it mod.rs

from the book

src/front_of_house/hosting.rs (what we covered)_
src/front_of_house/hosting/mod.rs (older style, still supported path)

If you use both styles for the same module, you’ll get a compiler error. Using a mix of both styles for different modules in the same project is allowed, but might be confusing for people navigating your project.

The main downside to the style that uses files named mod.rs is that your project can end up with many files named mod.rs, which can get confusing when you have them open in your editor at the same time.

[nitisht]

@nitisht Looks all good to me but one small thing is that we should keep src/rbac.rs on top level instead of moving it mod.rs

from the book

src/front_of_house/hosting.rs (what we covered)_
src/front_of_house/hosting/mod.rs (older style, still supported path)
If you use both styles for the same module, you’ll get a compiler error. Using a mix of both styles for different modules in the same project is allowed, but might be confusing for people navigating your project.
The main downside to the style that uses files named mod.rs is that your project can end up with many files named mod.rs, which can get confusing when you have them open in your editor at the same time.

I see..updated the PR accordingly