Support tags for generated API docs

[Jinming Yue]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind feature

What happened:

What you expected to happen:

In OpenAPI specification, tags can be used for logical grouping of operations by resources or any other qualifier.

Support tags for generated API docs.

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:
/assign