[bitbucket] conditional steps and changesets attribute

[bradrydzewski]

Harness currently supports limiting Pipeline execution based on changed files, however, this is only supported through triggers. It is not support at the Stage or Step level. Here is an example of the Bitbucket syntax at the stage level [1]:

pipelines:
   default:
    - stage:
        name: Build and test
        condition:
          changesets:
            includePaths:
              # only xml files directly under path1 directory
              - "path1/*.xml"
              # any changes in deeply nested directories under path2
              - "path2/**"

And here is an example at the Step level:

pipelines:
  default:
    - step:
        name: step1
        script:
            - echo "failing paths"
            - exit 1
        condition:
            changesets:
                includePaths:
                  # only xml files directly under path1 directory
                  - "path1/*.xml"
                  # any changes in deeply nested directories under path2
                  - "path2/**"

[1] https://support.atlassian.com/bitbucket-cloud/docs/stage-options/#Changesets
[2] https://support.atlassian.com/bitbucket-cloud/docs/step-options/#Condition-changesets

[hemanthmantri]

We have conditions at step and stage level which I think can leverage the PR payload. Also, the triggers should move to pipeline YAML for simplicity and ease of management.