Implement api using net/http from go 1.22 instead of gin

[oversize]

With the release of go 1.22 significant enhancements landed in the net/http package. These would allow to implement the api using the standard library only, removing the dependency to the gin framework.

[agaffney]

Just to note, we want to try to support the latest 2 minor Go toolchain versions everywhere, so we wouldn't want to require 1.22 features until 1.23 was out (and maybe had a few patch-level releases)