fix the oidc instructions to update deprecated MS Entra steps

[conceptualshark]

Description

The OIDC page references the app manifest in Azure AD Graph format, which has been deprecated and now now longer accessible as of January 7: https://learn.microsoft.com/en-us/entra/identity-platform/azure-active-directory-graph-app-manifest-deprecation#convert-an-app-manifest-in-azure-ad-graph-format-to-microsoft-graph-format

This PR updates the link to the new steps, updates the attribute to the correct reference, and updates the example to the new attribute name.

Internal slack: https://camunda.slack.com/archives/C026U8GBNSW/p1737545424357219

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support. (add bug or support label)
• This is already available but undocumented and should be released within a week. (add available & undocumented label)
• This is on a specific schedule and the assignee will coordinate a release with the DevEx team. (create draft PR and/or add hold label)
• This is part of a scheduled alpha or minor. (add alpha or minor label)
• There is no urgency with this change (add low prio label)

PR Checklist

• My changes are for the next minor and are in /docs directory (aka /next/).
• My changes are for an already released minor and are in /versioned_docs directory.

• I added a DRI, team, or delegate as a reviewer for technical accuracy and grammar/style:
  • Engineering team review
  • Technical writer review via @camunda/tech-writers unless working with an embedded writer.

[mesellings]

Lgtm - no changes - nice job! 🔥 🚀

[akeller]

I added the low prio label based on the checklist, but this looks more like a bug. I would like to see this fixed ASAP, if possible, as it looks like a quick win to review and merge. However, I'm not confident I can provide a review for technical accuracy.

[Ben-Sheppard]

Looks good from my side :) - I just wanted to double check one of our test apps in Entra and these instructions match! Thank you for handling this @conceptualshark