* Adding Occurences transformer

* Adding test for Occurences Transformer

* Cleanup. Adding a test.

* Adding doc

* Modifying UI to support custom calculations options

* Implementing data transformation

* Finalizing calculations implementation

* Cleanup

* Using Fields instead of arrays in data grouping

* Renaming transformation to GroupBy

* Adding some doc

* Apply suggestions (solving TS typing errors)

Co-authored-by: Marcus Andersson <systemvetaren@gmail.com>

* Tweaking UI

* Preventing of selecting twice the same field name.

* Removing console print. No calculations by default.

* Forgot to add the current value to the GroupBy selector

* Solving some typing issues and prettyfier errors

* Cleanup

* Updating test

* Ensure proper copy of options (solves some issues)

* Check if the fields exist in the data before processing

* Adding missing import in test file

* If group by field not specified, return all data untouched.

* Adding another missing import in test

* Minor updates

* Implementing GroupBy multiple fields + Improve field typing

* Removing console prints

* Allowing the exact number of fields to be added as aggregation

* Centering remove button icon

* Cleanup

* Correcting TS error

* Chaging transformer options structure

* Sorting so GroupBy fields appear on top

* Cleanup

* Simplifying some operations. Adding curly brackets.

* Changing some labels on the UI

* Updating test

* Cleanup

* Updating doc

* Fixed field list. Storing options as Record instead of Array.

* Update test

* Cleaned up the group by editor UI code.

* changed the transform to a table layout instead of a flexbox layout.

* cleaned up group by transformer.

* removed unused imports.

* Added some more tests.

* Added one more test and cleaned up code.

* fixed failing test.

* Fixed so we we have the proper casing on naming.

* fixed so we don't wrap on the first row.

Co-authored-by: Marcus Andersson <systemvetaren@gmail.com>
Co-authored-by: Torkel Ödegaard <torkel@grafana.com>
Co-authored-by: Marcus Andersson <marcus.andersson@grafana.com>