Use new standalone tbot docker image

[gawertm]

In Teleport v15.1.0, there now standalone tbot Docker image, which is 80% less in image size compare to teleport image.

We now ship a new container image that contains tbot but omits other Teleport binaries, providing a light-weight option for Machine ID users.

Requirements

• [x] Add to retagger
• [x] Update to use standalone image where tbot is deployed (teleport-operator, cluster-test-suites, etc)

References:

• https://github.com/gravitational/teleport/issues/21280#issuecomment-1916891243

[gawertm]

also bump teleport to v15