[CLOUDS-5524] Update Azure Integration manual app registration instructions

[parsons90]

What does this PR do? What is the motivation?

1. Removes the reference to redirect URIs. They are no longer required for creating app registrations and are not needed.
2. Removes "Datadog" from "Accounts in this organizational directory only". This is a quote from the app registration creation page in the Azure portal (see screenshot below). It only says "Datadog" because I was logged into the Datadog directory. For customers, it will use the name of their Azure directory. Having "Datadog" here can be confusing.

Merge instructions

Merge readiness:

• Ready for merge

Merge queue is enabled in this repo. To have it automatically merged after it receives the required reviews, create the PR (from a branch that follows the <yourname>/description naming convention) and then add the following PR comment:

/merge

Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/rebecca.parsons/CLOUDS-5524/update_manual_app_registration_instructions/integrations/guide/azure-manual-setup