feat: allow regex patterns in promql/aggregate keep and strip parameters

[Nepomuk5665]

Summary

This PR implements issue #509, allowing users to specify regex patterns in the keep and strip parameters for the promql/aggregate check.

Changes

• Modified AggregationCheck to accept a regex pattern for label matching instead of requiring literal strings
• Added extractLiteralLabels helper to extract individual labels from simple alternation patterns like job|instance
• Updated config validation to verify regex patterns in keep/strip lists
• For simple literal patterns, the behavior is fully backward compatible
• For regex patterns, all labels in src.Labels that match the pattern are checked

Example Usage

rule {
  match {
    kind = "alerting"
  }

  aggregate ".+" {
    keep = ["job|instance"]  # Preserve either job or instance labels
  }
}

Fixes #509