Update Astro Entra ID SCIM docs to reference Astro gallery app docs

[chomipi88]

Issue Type

Inaccurate, misleading, or out-of-date information

Links to Affected Docs

https://docs.astronomer.io/astro/set-up-scim-provisioning?tab=ME-ID#setup

The Issue or Context

Update our existing docs to reference the docs for the Astro gallery app: https://learn.microsoft.com/en-us/entra/identity/saas-apps/astro-provisioning-tutorial

Fix or Proposed Change

We should still include details how to get the Tenant URL and Secret Token (Step 6, item 6), which we have documented here and here

We should also retain the mapping tables as reference to the default configuration created by the gallery app.

We should also retain the WARNING as it still applies.

Additional Notes

No response

Required Reviewers

chomipi88, aliotta