Add FE API functions to generate and delete expert agent credentials

[Steve-Mcl]

Description

Merges into expert/pubsub backend branch - that should be reviewed and merged first

This pull request adds support for managing credentials that allow the BE Expert agent to connect to the platform

Expert Agent Credentials Management:

• Added two new API methods in admin.js: generateExpertAgentCreds to generate credentials and deleteExpertAgentCreds to delete them, both interacting with new backend endpoints. [1] [2]
• Updated the admin settings UI in General.vue to include a checkbox for enabling/disabling Expert agent access, dialogs for displaying generated credentials, and confirmation for disabling access.

Other:

• Updated General.vue to manage the enabled / disable credentials
• Registered the new setting key 'platform:expert-agent:creds' in the list of valid settings.

Related Issue(s)

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.95%. Comparing base (07c280b) to head (cd96ffb).

Additional details and impacted files

@@              Coverage Diff               @@
##           expert/pubsub    #7009   +/-   ##
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  Coverage          75.95%   75.95%           
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  Files                403      403           
  Lines              20435    20435           
  Branches            4928     4928           
==============================================
  Hits               15522    15522           
  Misses              4913     4913           

Flag	Coverage Δ
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