Requires #6881

GIVEN an upgrade has been triggered from <version A> to <version B> at a time t0
WHEN Elastic Agent creates the update marker AND
rollback.window > 0
THEN newly created update marker contains an entry under rollbacks_available similar to

details: 
  target_version: `<version B>`
  metadata: {}
 rollbacks_available:
      - version: `<version A>`,
        home: data/elastic-agent-<Version A>-<Version A commit hash>
        valid_until: "<t0 + agent.settings.upgrade.rollback.window>"

GIVEN an upgrade has been triggered from <version A> to <version B> at a time t0
WHEN Elastic Agent creates the update marker AND
rollback.window == 0
THEN newly created update marker will not contain an entry under rollbacks_available