[FEATURE] Support versioned documentation site

[sergio-sisternes-epam]

Problem

The documentation site is deployed on every merge to main, but users install APM from published releases. This creates a window where the docs reference features that don't yet exist in the latest release binary, leading to confusion and bug reports.

Real example: #641 -- a user on v0.8.11 followed the docs for apm marketplace add --host, which was documented after PR #589 merged to main but before a new release was cut. The --host option didn't exist in their installed version, so they filed a bug.

Proposed solution

Support multiple documentation versions:

• latest -- built and deployed on every merge to main (current behavior, unchanged)
• vX.Y.Z -- built and deployed on each GitHub release, matching the published binary

The default landing page should point to the latest stable release version, with a version switcher allowing users to navigate to latest (for contributors/pre-release) or any prior release.

Suggested approach

Starlight (the current doc framework) supports this via plugins or build-time configuration. The general pattern is:

1. On release tag push, build docs from that tag and deploy to a versioned path (e.g., /v0.8.12/)
2. On merge to main, build and deploy to /latest/
3. Add a version dropdown to the site header
4. Default root URL redirects to the latest stable release

Alternatives considered

• Banner warning on latest: Add a notice like "You are viewing unreleased documentation" -- simpler but doesn't fully solve the problem since users land on latest from search engines.
• Only deploy docs on release: Would eliminate the mismatch but delays documentation for contributors and reviewers.

[danielmeppiel]

A bit of a killer for now. We should quickly just move docs release pipeline to the binary release pipeline, supporting only 1 version of the docs at a time but at least making sure we update it only upon releasing a new apm version. That's step 1, immediately doable. Will revisit a versioned docs from v1.0 onwards.