issue regex: add field to match hostname regex

In some cases is good to be able to match an specific failure message only to specific hosts.

For example when we fail to fetch a test from pek2 servers...

Add a new input to https://gitlab.com/cki-project/datawarehouse/blob/c0240dd31ad897b5fd02946d914c2f3263c73b37/datawarehouse/templates/web/issue_regex.html and https://gitlab.com/cki-project/datawarehouse/blob/c0240dd31ad897b5fd02946d914c2f3263c73b37/datawarehouse/views.py

and integrate them in https://gitlab.com/cki-project/cki-tools/blob/9b09a36693a1ae2245a9119aec4ecbf3caad0807/cki/triager/checkers.py .

Make sure to cover the regex serializers in https://gitlab.com/cki-project/datawarehouse/blob/3476dbc672a2a19b95de1cbbbc1224ed0c11717f/datawarehouse/serializers.py

Jira: CKI-7034