Document HOTKEYS hot key detection command (GET/RESET)

[alon-arenberg]

Document the HOTKEYS command (server-side hot key detection)

Documentation for the server-side hot key detection feature added in
valkey-io/valkey#3708.

Hot key detection samples client key accesses and maintains an approximate
top-K of the most frequently accessed keys (Space-Saving algorithm) over a
fixed, frozen reporting window, surfaced through a new HOTKEYS container
command.

What's included

Command pages:

• commands/hotkeys.md — container overview: what hot key detection does,
  that it is disabled by default, and how to enable it (hotkey-top-k set to a
  positive value; 0 disables).
• commands/hotkeys-get.md — HOTKEYS GET: returns the hottest keys from the
  last completed window ordered by estimated QPS (descending); documents the
  key/db/qps fields and the QPS estimate, the frozen-window semantics
  (empty until the first window completes), the hotkey-top-k cap, and the
  RENAME/MOVE/SWAPDB stale-attribution behavior.
• commands/hotkeys-reset.md — HOTKEYS RESET: clears the live and frozen
  windows.

Reply metadata:

• resp2_replies.json / resp3_replies.json — reply descriptions for
  HOTKEYS, HOTKEYS GET, and HOTKEYS RESET. HOTKEYS GET returns an array
  of entries (RESP3: each entry is a map with key, db, qps; RESP2: the
  equivalent flat field/value array), ordered by QPS descending.

Related

• Feature PR: Add server-side hot key detection valkey#3708
• Clears the needs-doc-pr label on that PR.

Notes

The command metadata (arity, args, flags) is generated from the command JSON in
the main repo, so this PR only adds the human-readable pages and reply
descriptions.