Style: Enforce maximum of 2 import groups for go files

There isn't a whole lot of direction from the go project or tools for this.
A quick google search did turn up 2 projects that also document 2 groups, both
[Uber] and [CockroachDB].
We do have both goimports and gofumpt splitting stdlib vs others out if they
are mixed. But they don't do any futher kind of grouping. So in the absence of
concrete handling lets just settle on 2 because its easy to enforce. The script
below deletes newlines within `import ( ... )` blocks and then runs gofumpt which
will split and sort 2 at most 2 groups.

[Uber]: https://github.com/uber-go/guide/blob/22f61e283ac2f75ba34b62f565581cc70e35fb7a/style.md#import-group-ordering
[CockroachDB]: https://web.archive.org/web/20210509102622/https://wiki.crdb.io/wiki/spaces/CRDB/pages/181371303/Go+Golang+coding+guidelines#Import-Group-Ordering

Signed-off-by: Manuel Mendez <[email protected]>

CONTRIBUTING.md

@@ -98,6 +98,12 @@ One must support their proposed changes with unit tests.
 As you submit a pull request(PR) the CI generates a code coverage report.
 It will help you identify parts of the code that are not yet covered in unit tests.
 
+#### Go
+
+##### Import Groups
+
+There should be two groups of import blocks, one for stdlib and the other for everything else.
+
 ## Understanding code structure
 
 This is a nonexhaustive list important packages that happen to cover most of the code base.

ci-checks.sh

@@ -28,6 +28,10 @@ if ! nixfmt shell.nix; then
 	failed=1
 fi
 
+if ! git ls-files '*.go' | xargs -I% sh -c 'sed -i "/^import (/,/^)/ { /^\s*$/ d }" % && gofumpt -w -s %'; then
+	failed=1
+fi
+
 if ! git diff | (! grep .); then
 	failed=1
 fi