[JENKINS-57571] Configuration-as-Code compatibility

[cpoenisch]

Add full support for the Jenkins Configuration as Code Plugin. This mainly includes the global configurations for ECU-TEST installations and TEST-GUIDE servers.

Example configurations:

ECU-TEST

tool:
  ecu-test:
    installations:
    - home: "C:\\Program Files\\ECU-TEST 8.0"
      name: "ECU-TEST 8.0"

TEST-GUIDE

unclassified:
  test-guide:
    installations:
      - config:
        settings:
          - atx-boolean-setting:
            group: UPLOAD
            name: "uploadToServer"
            value: true
          - atx-text-setting:
            group: UPLOAD
            name: "serverURL"
            value: "127.0.0.1"
          - ...
        customSettings:
          - atx-custom-boolean-setting:
            name: "customOption"
            checked: true
          - atx-custom-text-setting:
            name: "customLabel"
            value: "test"
          - ...
      name: "TEST-GUIDE"
      toolName: "ECU-TEST"

Tracking: jenkinsci/configuration-as-code-plugin#809

[oleg-nenashev]

Also a placeholder for the JCasC compatibility dashboard: https://issues.jenkins-ci.org/browse/JENKINS-57571