Address Identity UI differences for 8.6 and 8.7

[akeller]

Description

Follow up to #5331.

• Updates UI descriptions, including sentence case buttons/tabs
• Removes (outdated) screenshots on these pages

Reviewers, please ensure I have button and tab names correct and correctly cased.

Important topics that should be revisited outside the scope of this PR:

• How and when do we document the empty state? (Is it realistic that Identity users would see some empty states, even during pilot/PoC?)
• Do we reintroduce screenshots, and how do we keep them maintained? (https://github.com/camunda/documentation-team/issues/469?)

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 an upcoming minor release and:
  • are in the /docs directory (version 8.8).
  • are in the /versioned_docs/version-8.7/ directory (version 8.7).
• 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.

[github-actions]

👋 🤖 🤔 Hello, @conceptualshark! Did you make your changes in all the right places?

These files were changed only in versioned_docs/version-8.7/. You might want to duplicate these changes in docs/.

• versioned_docs/version-8.7/self-managed/identity/user-guide/groups/manage-groups.md
• versioned_docs/version-8.7/self-managed/identity/user-guide/groups/manage-users-roles-to-group.md
• versioned_docs/version-8.7/self-managed/identity/user-guide/roles/manage-permissions.md
• versioned_docs/version-8.7/self-managed/identity/user-guide/roles/manage-roles.md

These files were changed only in versioned_docs/version-8.6/. You might want to duplicate these changes in docs/.

• versioned_docs/version-8.6/self-managed/identity/user-guide/groups/manage-groups.md
• versioned_docs/version-8.6/self-managed/identity/user-guide/groups/manage-users-roles-to-group.md
• versioned_docs/version-8.6/self-managed/identity/user-guide/roles/manage-permissions.md
• versioned_docs/version-8.6/self-managed/identity/user-guide/roles/manage-roles.md

You may have done this intentionally, but we wanted to point it out in case you didn't. You can read more about the versioning within our docs in our documentation guidelines.

[conceptualshark]

Docker behaved long enough that I was able to verify the tab/button names. I updated a few areas that didn't make sense without the image, and added a h2 to the permissions so explaining what a "definition" was could just link there.

This seems to be accurate to me, though! Goodbye images!

[FarkasRabai]

Great! Thank you!

[github-actions]

🧹 Preview environment for this PR has been torn down.