golang: Add go version 1.18

Go 1.18 is the incremental improvement for earlier go 1.17 release.
Is "is a significant release, including changes to the language,
implementation of the toolchain, runtime, and libraries". Please find
all details in the official release note:

    https://go.dev/doc/go1.18

It was released on 2022-03-15. Due to the go promise of compatibility
most software should still compile without any problems.

/reviewed-on nexedi/slapos!1305