XX-11199: Expose REST API for Page groups management

- api/pagegroups GET for retrieving all page groups defined in system, POST to create new one
- api/pagegroups/{pageId} GET, DELETE, PUT for retrieving, deleting and modifying page groups based on page group id
- api/pagegroups/settings to manage general service options (GET, DELETE, PUT by setting path)
- api/pagegroups/prompts GET for list of orbit prompts, POST to upload new prompt
- api/pagegroups/prompts/{promptName} GET to download prompt based on file name, DELETE to delete prompt
- api/pagegroups/prompts/{promptName}/stream to stream prompt