Add prometheus metrics for health check results.

[Kircheneer]

Closes: DNE

What's Changed

Exposes metrics for the health check results under /metrics as follows:

# HELP health_check_database_info Multiprocess metric
# TYPE health_check_database_info gauge
health_check_database_info 1.0
# HELP health_check_cache_ops_redis_info Multiprocess metric
# TYPE health_check_cache_ops_redis_info gauge
health_check_cache_ops_redis_info 0.0
# HELP health_check_redis_backend_info Multiprocess metric
# TYPE health_check_redis_backend_info gauge
health_check_redis_backend_info 1.0

I have defaulted to enabling the metrics endpoint in the development configuration. I am happy to change this back if you want.

I have explicitly added

# Custom prometheus metrics
prometheus-client = "~0.14.1"

to pyproject.toml. This is a transitive dependency through django-prometheus, so it is not technically a new dependency,

TODO

• Explanation of Change(s)
• Added change log fragment(s) (for more information see the documentation)
• Attached Screenshots, Payload Example
• Unit, Integration Tests
• Documentation Updates (when adding/changing features)
• Outline Remaining Work, Constraints from Design

[Kircheneer]

For some reason the cache ops health check always seems to fail, but that health check is not included in the (default) /health endpoint anyway, possibly its broken?

[bryanculver]

For some reason the cache ops health check always seems to fail, but that health check is not included in the (default) /health endpoint anyway, possibly its broken?

Well we are ripping out Cacheops in 2.0 and it's already been disabled by default for new installs in 1.5.

What is the intended consumer of the /metrics endpoint?

[Kircheneer]

What is the intended consumer of the /metrics endpoint?

Prometheus/Telegraf for telemetry purposes.