Merge branch '517768-case-insensitive-labels-autocomplete' into 'master'

Make multi-word label matching case-insensitive

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/180823



Merged-by: Heinrich Lee Yu <heinrich@gitlab.com>
Approved-by: Lindsey Shelton <lshelton@gitlab.com>
Approved-by: Tomas Bulva <tbulva@gitlab.com>
Approved-by: Costel Maxim <cmaxim@gitlab.com>