adopt stable tags for runner images

[freeznet]

Function Mesh releases various runner images across Pulsar 2.8 to 2.11 (3.0 is coming soon), with a lot of runner images, the users will need to keep updating the runner image to the latest for specific branches.

We should adopt the stable tags set for runner images, to ease kind of pain when struggle with the runner image tags.

For example:

For Branch 2.8, we will need to introduce a 2.8 tag and a 2.8.x tag to the latest release.

To make sure a better debug purpose, we will need to expose the actual version to the image, such as via the ENV.