Feat: Rbac into auth section

[Guaris]

Description

Fixes #304

Preview Links

Checklist

• Every page is page one.
• Tested how-to docs. If not, note why here.
• All pages contain metadata.
• Updated sources.yaml. For more info, review track docs changes
• Any new docs link to existing docs.
• All autogenerated instructions render correctly (API, decK, Konnect, Kong Manager).
• Style guide (capitalized gateway entities, placeholder URLs) implemented correctly.

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[lena-larionova]

Blocked for now, do not merge. Needs a discussion on where this content belongs, url structure, and how we define "gateway entities".