docs: Change UI text 'master' to 'control plane'.

Created by: patrickluoyu

Signed-off-by: Patrick-LuoYu patrickluo@yunify.com

What type of PR is this?

/kind documentation

What this PR does / why we need it:

Change UI text 'master' to 'control plane'.

Special notes for reviewers:

/assign @harrisonliu5 @xuliwenwenwen Please take a look. Thanks!

Does this PR introduced a user-facing change?

None