125276: kvserver: constrain store gossip chatter r=nvanbenschoten a=kvoli

Previously, it was possible that store's would gossip their store
descriptors rapidly on capacity changes, without limit. This patch
introduces a hard frequency limit of 2s on capacity change triggered
gossip. In other words, irrespective of any capacity changes that may
have taken place, a store will gossip at most every 2s if satisfying the
capacity delta trigger.

Resolves: #125210
Release note: None


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Increase the relative requirement for triggering store gossip on
capacity changes for lease and ranges. Previously, the requirement was a
+-5% delta from the previously gossiped value, in addition to a minimum
(5). Increase the relative delta from 5 to 10%.

Informs: #125227
Release note: None

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Introduce `kv.store_gossip.capacity_delta_threshold` and
`kv.store_gossip.max_frequency`, which control the capacity delta
required to trigger eager gossip for lease/range counts and the maximum
frequency of eager store gossip.

The defaults for these settings remained unchanged from the previously
hard-coded defaults:

`kv.store_gossip.capacity_delta_threshold`: 0.10
`kv.store_gossip.max_frequency`: 2s

Resolves: #125227
Release note: None

Co-authored-by: Austen McClernon <austen@cockroachlabs.com>