Update /goal in Agentic Chat docs for GA

Enrique Alcántararequested to merge
633466-goal-command-ga-docs into master

What does this MR do and why?

Updates the /goal section of the Duo Agentic Chat docs for general availability.

  • Records that duo_chat_goal_command was enabled by default in 19.5. The history still said the flag was disabled by default.
  • Adds the GA entry for 19.6, where !267398 (merged) removes the flag.
  • Removes the [!flag] callout, which no longer applies.

Split out of !267398 (merged) so the flag removal and the docs land as separate reviews.

Anchor check

The issue asks to confirm the anchor the release post links to still matches the heading. It does not, and this MR deliberately leaves the heading alone:

  • The heading is Start a long-running task with the /goal command, so the anchor is #start-a-long-running-task-with-the-goal-command. It is already published for 19.5.
  • The release note in !260813 (closed) links to #work-toward-a-goal.

That MR is still a draft, so fixing the link there is cheaper than renaming a published heading and breaking the existing anchor.

Resolves #633466 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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