feat: add lokitool

[MichelHollands]

What this PR does / why we need it:

• Copy across the rules part from cortex-tool and add it to a new lokitool binary.
• Add a makefile target: make lokitool
• Fixed the linter issues of the copied code
• Removed the backend parameter
• Renamed things from Cortex to Loki
• Removed Cortex specific tests

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
  • If the change is worth mentioning in the release notes, add add-to-release-notes label
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[JStickler]

[Docs team] Just looking at the markdown (.md) files, it doesn't look like the references to "cortex" in the user docs have been updated. Was that an oversight, or were you planning to update the docs in a separate PR?

[MichelHollands]

[Docs team] Just looking at the markdown (.md) files, it doesn't look like the references to "cortex" in the user docs have been updated. Was that an oversight, or were you planning to update the docs in a separate PR?

This was an oversight. This PR is already so big I stopped working on it for now. More PRs will follow to get this into shape. One fixing references to cortex will be one of them. Thanks for letting me know.

[Skaronator]

Will this be available as a dedicated container image? It would be pretty useful for all the CI pipeline users :)

[JStickler]

@Skaronator When I asked, the response I got was "No plans, but PRs are always welcome!"