Adds an option to switch to an advanced (JSON) editor when creating an analytics job.

This builds upon the previous work for the modal for analytics job creation and the use of useReducer():

- The files of the custom hook useCreateAnalyticsForm() have been further split up and there's now separate actions.ts and state.ts files.
- To only allow updating what's really related to the form value's state via setFormState, the state structure has been updated and more fine grained actions have been added.
- The user can enabled the advanced editor, but cannot move back to the original form (there's a help text in the UI about that).
- The advanced editor component's (CreateAnalyticsAdvancedEditor) structure is based on the regular form, it still has an input field for the job ID and the toggle for optionally creating an index pattern. The fields for source/destination index are replaced by an editable JSON textarea input.
- The advanced editor features mostly the same validation like the regular form. For example, if the source index isn't valid, an error will be shown in a CallOut below the editable area.

…43989

…43989

…43989