What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind feature

What does this PR do / why do we need it:
This PR is to move 'multi-subgraphs' interface to internal

Which issue(s) this PR fixes:

Fixes #I1TSNS:[Auto parallel] 'multi-subgraphs' interface needs to be moved to internal

Special notes for your reviewers: