Add namespace option

[rajzik]

This is a fix of 2974.

I have already implemented fork of this repo and tested it with my adoption:
@rajzik/babel-plugin-styled-components.

It is working well and it creates a unique name with the given namespace.
This will resolve all issues with micro frontends class name duplication.

[pgangwani]

Dear core contributors,
Could you please review this PR?
This is the only option I see could work for me where I have micro-frontend setup composed using ESI at akamai (cdn). Please suggest if there is any other way which we are missing.

@mxstbr @probablyup @kitten

[bowsersenior]

I was looking for exactly this feature to solve a production bug with clashing class names generated by styled-components. It would be awesome to have this feature available!

[rajzik]

@bowsersenior as for now, I have released fork with namespace setting
plugin-namespace.
It is just fork with namespace added so you can substitute babel-plugin-styled-component with mine.
I am using it, and it works well.

[luanraithz]

I'm also having a production bug related to multiple styled-components instances conflicting.

[ghost]

this would also solve a lot of the issues i am having as well, ping again :P

[quantizor]

If someone could add some docs to the website, that'd be awesome: styled-components/styled-components-website#696