feat(helm): add replicas to loki-canary deployment

[demon]

What this PR does / why we need it:
Currently, there's no middle ground between deploying the canary as a single replica or deploying to your entire cluster. For very large clusters, this can result in a lot of pressure on Loki. But using a single canary replica doesn't give a huge amount of confidence on the health of the deployment.

Default to 1 replica so this is a no-op change for existing setups.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• 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

[jkroepke]

LGTM - make sense

[JStickler]

@demon Please generate Helm Chart reference by running 'make -C docs sources/setup/install/helm/reference.md` and then checking in the update.

[Jayclifford345]

LGTM! ~ Set to automerge once all tests pass

The above Helm reference update still needs to be done.

[JStickler]

@demon still needs to generate Helm Chart reference by running 'make -C docs sources/setup/install/helm/reference.md before we can get this passing the tests.

[Jayclifford345]

Hey @demon, I would love to merge this but the docs still need to be regenerated