[Feat]: Improving docs site with versions

[matglas]

Describe the solution you'd like:

Implement a way for us to have docs per version of Witness.

User value:

This allows a user to see the specific cli reference and schema while at the same time we can iterate on new things.

**Expected **

On the docs site you would be able to select the version you want to view. This could be thru a drop down menu.

Proposed solution:

• We build a latest version from master.
• Docs for 0.7.0 would be on branch docs/0.7.0
• Docs for 0.6.0 would be on branch docs/0.6.0 etc.

This also allows us to do needed fixes to older versions.