Inaccruate link text related to harbor versions

[jessehu]

The docs links on the top right of https://goharbor.io/ says 2.2.0, 2.1.0, 2.0.0, but actually the link points to docs for all version 2.2.x or 2.1.x. So it's better to change the link to to 2.2.x (or 2.2), etc.

The text "Harbor version 2.1.0" on https://goharbor.io/docs/2.1.0/ should also be "Harbor version 2.1.x".

[a-mccarthy]

We can update in the config.toml file to display the version number with .x instead of .0 in the drop down.

To change the version ion the docs page, we need to update docs/_index.md file for each version in the release branch (release-X.X.X) as well as the master branch