jobs: introduce JobKind enum
Instead of hardcoding the strings everywhere, which can be error prone.
Signed-off-by: Arturo Borrero Gonzalez aborrero@wikimedia.org Change-Id: Ie158d3538625a9d1b9f7b518f55bcf61abae059a
[ NOTE: this was rescued and refreshed from an old patch in gerrit https://gerrit.wikimedia.org/r/c/cloud/toolforge/jobs-framework-api/+/909307 ]