Read API scope support

[shikher-srivastava]

Feature enhancement for #118
Added a scope configuration property replacing hard-coded 'api' to allow customizing the OAuth scopes requested during login.
Added an "OAuth Scope" dropdown menu.
Added a dedicated help.html,
The default choice safely remains api to preserve backwards compatibility.

Testing done

Verified backwards compatibility for api and tested read_api scoped client token by installing the packaged hpi into an existing jenkins controller.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed