Add support for newer Authentik "entitlements" header

[dmptrluke]

Proposed change

Hi there. This adds default support for a new header that Authentik sends for the entitlements feature.

Example:
You can add an entitlement named "admin" to an Authentik application, bind that entitlement to any group you desire, and Authentik will send:

X-Authentik-Entitlements: admin

This can then be used a clean role header for Frigate auth

Documentation:

https://docs.goauthentik.io/add-secure-apps/providers/proxy/#x-authentik-entitlements
https://docs.goauthentik.io/add-secure-apps/applications/manage_apps/#application-entitlements

This has not been run through full tests because it is not a change to the Authentik code itself. I don't have a full Authentik development environment set up at this time.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code
• Documentation Update

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• UI changes including text have used i18n keys and have been added to the en locale.
• The code has been formatted using Ruff (ruff format frigate)

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