use a proper struct to decode the config

[Nexucis]

fix #193

[slrtbtfs]

So what's happening here is:

• The gopls lib unmarshals the JSON received by the client.
• This code marshals and unmarshals part of it again, as a somewhat weird way of typecasting.

While I'm not principally against this, it should at least be documented, what is going on and why it has been done this way.

[Nexucis]

as a comment or as a markdown documentation ?

[slrtbtfs]

Comment should be fine.

[Nexucis]

done