[docs] Update aspire wait and aspire describe docs for reusable resource observation

[aspire-repo-bot]

Documents changes from microsoft/aspire#19567

@adamint

Targeting release/13.6 based on the source PR milestone 13.6.

Why

PR #19567 refactors CLI resource observation into a reusable, typed
ResourceWaitService and reworks ResourceSnapshotWatcher to use a single
coalesced subscription for both initial state and subsequent updates. Two
user-visible behavior changes result:

• aspire wait <resource> --status down now fails (exit code 18) if the
  resource enters FailedToStart, instead of treating that as a successful
  "down" outcome. The wait service applies one monotonic timeout and always
  treats FailedToStart as terminal failure, "even when waiting for a
  resource to be down" (PR description).
• aspire describe --follow now emits the current state of every resource
  immediately when streaming starts (closing the previous snapshot/watch gap),
  even if no later change occurs, in addition to streaming subsequent updates.

Changes

• reference/cli/commands/aspire-wait.mdx:
  • Updated the exit-code table entry for code 18 to say the resource entered
    FailedToStart, regardless of the target status (previously scoped to
    "waiting for up or healthy").
  • Added a sentence to the Description section clarifying that a
    FailedToStart resource always fails the wait, even when the target
    status is down.
• reference/cli/commands/aspire-describe.mdx:
  • Updated the --follow option description to state that the current state
    of every resource is emitted immediately when streaming starts, even if no
    further changes occur.

No new commands, flags, or public docs-relevant types were introduced by this
PR that require new pages — the new KnownResourceStates well-known states
(FailedToStart, etc.) were already documented on
extensibility/custom-resources.mdx prior to this PR (the type itself just
moved files internally).

Generated by PR Documentation Check for #19567 · auto · 94.5 AIC · ⌖ 10.2 AIC · ⊞ 19.6K · ◷

[aspire-repo-bot]

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