feat: Ability to add labels with constant values

[DanArmor]

Example: we have application with different environments, each having its own exporter. We want to distinguish metrics by environment by label, not by metric prefix. So we need to provide exporter with an ability to attach custom labels to metrics.

Implemented as cli arg --static-label, that can be provided multiple times in format --static-label key=value

Example: python cli.py --broker-url=redis://127.0.0.1:6379 --static-label application=my-application-name --static-label environment=staging

Here is the result:

Code changes:

• New cli arg
• In the code where metrics are defined, there are *self.static_label_keys at the end to unpack provided static labels names
• In the code where we provide labels for metrics now there are **self.static_label, which unpack static labels and their values.

[danihodovic]

mildly related #323

[danihodovic]

Can you add tests?

[DanArmor]

Can you add tests?

Yes, I will add them soon and mention you when I'm done

[DanArmor]

@danihodovic I've added tests

• To test static labels we need to create new exporter instance with static labels provided at creation (to not pollute already existing tests by providing static labels to existing exporter, used in all other tests)
• Common exporter configuration separated into exporter_cfg_defaults fixture, used in exporter_instance and exporter_instance_static_labels fixtures
• To test static lables I've made test_integration_static_labels by duplicating of test_integration with changes to labels checks to test static labels
• Disabled too-many-statements check for test_integration_static_labels, because it's complaining about overstepping statement limit by 1 statement (51/50)

[danihodovic]

Thank you. Released as 0.11.0

https://hub.docker.com/layers/danihodovic/celery-exporter/0.11.0/images/sha256-28168e56392250ba5e01faa691c4fd890d90f737dfdcbeeba60de40e4e9dc440?context=explore