collator-alerting-rules

Alert manager collator rules for generic substrate metrics from the prometheus stream.

Most of the rules originate from the alerting-rules.yaml that are in the substrate repo.

customization:

Changed all of the applicable of polkadot_ to substrate_ metrics
Removed the authority_discovery metrics as this is not applicable to collator roles
Removed the label {{ $labels.entity }} as we don't know and have not configued such a label.
Added increase(substrate_proposer_block_constructed_count[1h]) < 1 to the rules to warn if you haven't constructed a block in a hour time-frame.

We might maintain and improve on these metrics in the future for more collator specific metrics.