fix(docz-core): use of src config in edit button link

[bpetetot]

Description

In version 0.9.2, when I have a src different from ./ in the .doczrc.js file, the edit button doesn't have the correct link address. The src is missing in the link.

For example:
With the following configuration:

#.doczrc.js
export default {
  src: './src',
  port: 3001,
}

A mdx file in myrepo/src/components/button/button.mdx

Then the edit button will go to:

https://github.com/xxx/myrepo/components/button/button.mdx

instead of:

https://github.com/xxx/myrepo/src/components/button/button.mdx

In this PR, I add the missing part of the link using the src config parameter.

[pedronauck]

Great @bpetetot, thank the pr, I'm merging it right now 🙏