Gateway advertisement names collide when rule or node names contain a dash #762

Summary

The gateway names each rule advertisement <rule>-<node>-v4 or -v6. A dash can appear inside both rule and node names, so two different rule/node pairs can produce the same name. Rule a-b on node c and rule a on node b-c both produce a-b-c-v4.

When that happens, two gateway nodes write the same BGPAdvertisement:

1. Each node's applyBGPAdvertisements sees the object exists and backfills its own galactic.datum.net/network-rule and galactic.datum.net/gateway-node labels and owner reference, so the labels flip on every pass.
2. Its prefixes flip between the two rules' VIPs.
3. withdrawRuleAdvertisements deletes by constructed name, so withdrawing one rule from one node deletes the other rule's advertisement.

Where

• Names built in applyBGPAdvertisements and withdrawRuleAdvertisements.
• isNodeAdvertisement also compares against the constructed name.

Reproduce

1. Two gateway nodes named c and b-c in one namespace.
2. NetworkRules a-b and a in that namespace, each loaded on a different one of those nodes.
3. Both nodes reconcile the same a-b-c-v4 BGPAdvertisement.

Expected

Every rule/node pair maps to its own advertisement. One option is to keep the readable prefix and append a short hash of the rule and node names, then select by the two labels everywhere instead of rebuilding the name.

Found while fixing #714 (#758).