E2e tests external broker

[cstns]

Description

Add e2e tests to cover the 3rd party broker creation/deletion. Also fixes a pre-defined input not getting selected due to type difference

Related Issue(s)

closes https://github.com/FlowFuse/flowfuse/issues/5103

Checklist

• [x] I have read the contribution guidelines
• [x] 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

Labels

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.31%. Comparing base (78114b8) to head (293f6bd). Report is 33 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5460   +/-   ##
=======================================
  Coverage   77.31%   77.31%           
=======================================
  Files         350      350           
  Lines       16583    16583           
  Branches     3865     3865           
=======================================
  Hits        12821    12821           
  Misses       3762     3762           

Flag	Coverage Δ
backend	77.31% <ø> (ø)

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