[Fleet] Add ability to specify which integration variables should be configurable

[Zacqary]

Summary

Closes #96319

Adds an optional flag called frozen to package policy input vars. When set through the Preconfiguration API, this will make it impossible to edit the specified variable.

This freezes the variable both in the UI and through the update API.

Note that EuiCodeEditor has no disabled prop, so I had to approximate this for yaml-type variables by conditionally rendering a disabled textarea with similar styling to the code editor:

Example

In kibana.dev.yml:

xpack.fleet.agentPolicies:
  - name: Preconfigured Policy From Config
    id: 1
    namespace: test
    package_policies:
      - package:
          name: system
        name: System Integration
        inputs:
          - type: system/metrics
            enabled: true
            vars:
              - name: system.hostfs
                value: home/test
                frozen: true
            streams:
              - data_stream:
                  dataset: system.fsstat
                vars:
                  - name: processors
                    frozen: true
              - data_stream:
                  dataset: system.core
                enabled: true
                vars:
                  - name: period
                    value: 20s
                    frozen: true
          - type: winlog
            enabled: false

Checklist

• Unit or functional tests were updated or added to match the most common scenarios
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)

[elasticmachine]

Pinging @elastic/fleet (Feature:Fleet)

[jen-huang]

Code LGTM, thanks for landing this so quickly 🚀

[ph]

Woa @Zacqary this is great thanks for making a quick change!

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: d5c027f
• Storybooks Preview

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
fleet	711.5KB	711.8KB	+372.0B

History

• 💚 Build #119721 succeeded 08c806b

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @Zacqary