Start using the new slog handlers. With this commit we also remove the
need for the LogWriter since we let our LogRotator implement io.Writer
and pass that in to our log file handler.
With go 1.17 a change to the build flags was implemented:
https://go.googlesource.com/proposal/+/master/design/draft-gobuild.md
The formatter now automatically adds the forward-compatible build tag
format and the linter checks for them, so we need to include them in our
code.