Move docindex.yml from steps -> jobs

[danieljurek]

This PR:

• Moves docindex.yml from the steps folder to the jobs folder because it is a collection of jobs, not templates
• Prepares for extension of docindex.yml file with additional docs.ms automations

Doc index pipelines for all languages will need to be updated:

• Put a pipeline yaml (docindex.yml) in eng/pipelines/ which uses the eng/common template yaml
• Update the existing pipeline in DevOps to use the eng/pipelines/docindex.yml instead of the template

[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[ghost]

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