Make time window parameters (`start`/`end`) for environment-specific alert metrics mandatory
Currently, the parameters for environment-specific alert metrics are optional.
After we finish #31368 (closed) and have frontend ready we might want to make these parameter mandatory in backend.
See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26228#note_152464515 for more code context.
Edited by Peter Leitzen