* feat(loki-variable-editor): replace input with select with datasource labels
* feat(loki-variable-editor): update test
* feat(loki-variable-editor): allow the editor to receive an existing query instance and edit it
* feat(loki-variable-editor): allow custom values in the label select
* feat(loki-variable-editor): mark stream field as optional
* feat(loki-variable-editor): add placeholder to stream selector and extend tooltip info
* feat(loki-query-editor): create base editor component
* feat(loki-query-editor): update editor to use loki query type
* feat(loki-query-editor): add custom variable support to datasource
* feat(loki-query-editor): prevent errors when no label is present
* Add unit test for LokiMetricFindQuery
* Update datasource test
* Add component test
* Add variable query migration support
* feat(loki-query-editor): add migration support for older-format variables
* Fix enum capitalization for consistency
* Move attribute to the top of the class
* Remove unnecessary from()
* Update capitalization of new enum
* Fix enum capitalization in component
* feat(loki-query-editor): replace unnecessary class with class method