Use release tags for the Trial images

[andreyvelich]

/kind feature

As discussed in the AutoML meeting at 2021-03-24, we decided to use the latest tag in the master branch and release tag in the release- branch for the Trial images.
Then, users can deploy examples for the specific Katib version and use the latest changes.

/cc @gaocegege @johnugeorge @yanniszark

[andreyvelich]

/assign @andreyvelich

[gaocegege]

LGTM!