plugin-fs: kill()/stop() not implemented on killable/pollable tasks

Sub-issue of kestra-io/kestra-ee#10964.

**Tasks:** io.kestra.plugin.fs.ssh.Command

**Why:** Blocks on a remote SSH channel until the command exits; no kill()/stop() to close the channel and abort the remote command.

**Fix:** override `kill()` and/or `stop()` on these task classes to cancel the poll loop / close the consumer / cancel the remote job. See `io.kestra.plugin.gcp.bigquery.AbstractBigquery` for a reference implementation.

Start with io.kestra.plugin.fs.ssh.Command and compare its task lifecycle with io.kestra.plugin.gcp.bigquery.AbstractBigquery. Trace how the SSH command blocks on the remote channel and identify the existing poll-loop, consumer, or remote-job handling. Done means kill() and/or stop() cancels the poll loop, closes the consumer, or cancels the remote job so the command can be aborted.

Written by the indexing model from the issue text.