HACK: report dataplane update events back to Typha for aggregation

[fasaxc]

Description

Hackathon entry.

• Send a new message from Typha to Felix with Typha's breadcrumb sequence number
• Plumb that through Felix all the way to the dataplane and then report it back to Typha after each apply (with rate limiting).
• In Typha, aggregate the stats and emit a histogram of dataplane apply latency every 10s.

Could lead on to:

• Adding OTEL for Typha updates.
• Adding prometheus metrics.
• Figuring out when the whole cluster is fully converged.

Related issues/PRs

Todos

• Tests
• Documentation
• Release note

Release Note

TBD

Reminder for the reviewer

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[fasaxc]

Productising part of this under #10918