feat(policies): Support global policy

[salvacorts]

What this PR does / why we need it:

This PR implements global policies that are applied to all streams (regardless of their stream<>policy mappings).

• For enforced labels: the global policy labels is appended to the named policy label if the stream matches a named policy. Otherwise only the global policy labels will be enforced if any.
• For blocked ingestion:
  • If the mapped policy is empty, the global policy block is applied (if exists).
  • If the mapped policy is not empty, the stream will be blocked only if there is a matching named policy block

E.g. If we have

block_ingestion_policy_until:
   "*": <eod>
   policy1: <eod>

• stream not matching any policy --> will be blocked due to global policy
• stream matching policy1 --> will be blocked due to policy1 policy
• stream matching policy2 --> won't be blocked since there is no block entry for policy2

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

[github-actions]

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[DylanGuedes]

couple of questions