Add support for musl in addition to gnu

[macnibblet]

Describe the solution you'd like
Would make a lot of peoples lives easier if we could provide a musl binary as well as the existing gnu one for linux so we can use it directly in an alpine image. This is already done for the rover project but not router :(

Describe alternatives you've considered
Right now we are using an ubuntu image specifically for running the router in k8s and it works but we would want to go back to alpine if possible.

[garypen]

Unfortunately this is not simple. We have a dependency on deno, which, as this issue illustrates, is musl averse.

For more details see #65.

[DGolubets]

I see that you are gradually rewriting JavaScript in Rust, e.g. query validation process in the last release.
Does that mean the router won't need Deno at some point?
Is there a list of features still using JavaScript?