release(http-action): promote 0.2.1 to stable

[rmyndharis]

http-action has been held at beta on one outstanding item: a manual install smoke on a real host, covering the checks that cannot be automated. That smoke has now been run in full and passed, so the status moves to stable. No behaviour changed in this release.

Verified against a live OpenWA 0.12.1 host with a connected WhatsApp session, an HTTP echo service upstream, and commands driven from a second connected number:

• install from package, configure, enable;
• a POST command with path and JSON-body templating — the reply carried the templated body, the sender's phone resolved from the message, and the configured bearer credential reached the upstream;
• a command whose upstream returns 404 — the not-found template was selected;
• a command whose upstream returns 500 — the error template was selected;
• disable and re-enable — configuration survived and a command worked afterwards;
• a host restart — the plugin came back enabled and a command was confirmed working afterwards, not merely reported as enabled.

With another responder plugin installed alongside, commands were answered by this plugin and non-command messages went to the other one, so the co-installation ordering behaves as documented.

testedOpenWAVersion is unchanged at 0.12.1. A stale sentence in the plugin README that described the status as beta and the plugin as not install-tested has been removed, since it now contradicts the shipped state.