kvserver: improve system lease observability

[erikgrinaker]

kvserver: add leases.liveness metric

This patch adds the metric leases.liveness tracking the number of liveness range leases per node (generally 1 or 0). This is useful to find out which node had the liveness lease at a particular time.

I ran a 10k range cluster to look at the CPU cost of the key comparisons, it didn't show up on CPU profiles.

Epic: none
Release note (ops change): added the metric leases.liveness showing the number of liveness range leases per node (generally 1 or 0), to track the liveness range leaseholder.

kvserver: log system range lease acquisition

This patch logs acquisition of meta/liveness range leases to the health log. These leases are critical to cluster health, and during debugging it's useful to know their location over time.

Resolves #99472.

Epic: none
Release note: none

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[erikgrinaker]

bors r+

[craig]

Build failed:

• Bazel Essential CI (Cockroach)

[erikgrinaker]

bors retry

[craig]

Build failed:

• Bazel Essential CI (Cockroach)

[erikgrinaker]

bors retry

[craig]

Build failed:

• Bazel Essential CI (Cockroach)

[erikgrinaker]

bors retry

[craig]

Build failed:

• Bazel Essential CI (Cockroach)

[erikgrinaker]

Wow, much flake.

bors retry

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

---

error creating merge commit from 71117b1 to blathers/backport-release-22.2-104008: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.2.x failed. See errors above.

---

error creating merge commit from b9148c7 to blathers/backport-release-23.1-104008: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 23.1.x failed. See errors above.

---

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}