feat: describe how to configure multiple identity providers

[romansmirnov]

Description

related to #6645

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 Documentation 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

• [ ] The commit history of this PR is cleaned up, using {type}(scope): {description} commit message(s)

• [ ] My changes are for an upcoming minor release and are in the /docs directory (version 8.9).
• [ ] My changes are for an already released minor and are in a /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.

[romansmirnov]

@StevePascoe, I (finally) documented how to configure multiple identity providers. Would you be available for a review?

[StevePascoe]

@romansmirnov -> That's funny. I took a stab at creating documentation on this today as well: https://github.com/camunda/camunda-docs/pull/7687

[romansmirnov]

@romansmirnov -> That's funny. I took a stab at creating documentation on this today as well: #7687

Ah nice! Sorry that I haven't made it transparent. Nevertheless, I could adjust my PR to only document the configuration options in the reference guide. WDYT?

[StevePascoe]

My apologies as well. I don't think I told you I was picking this up. Yeah, let's update yours to document the configuration options in the reference guide. I'll update mine to use 'provider-id' instead of registration-id and I'm going to use your examples.

One thing I did want to confirm with you is the login page behaviour. Is this statement true: "The cluster login page will show a list of available OIDC Providers. Users will see the client name as the selection, so choose accordingly."

[romansmirnov]

Yeah, let's update yours to document the configuration options in the reference guide.

@StevePascoe, I updated my PR, it is ready for review.

One thing I did want to confirm with you is the login page behaviour. Is this statement true: "The cluster login page will show a list of available OIDC Providers. Users will see the client name as the selection, so choose accordingly."

Yes, your understanding is correct.

[romansmirnov]

@StevePascoe, I applied your feedback and fixed the documentation in the other tables (describing the oidc properties) as well.