Enhance goimports linter to support opinionated go import statements

[sebastien-rosset]

Your feature request related to a problem? Please describe.

This is a proposal to enhance the goimports linter to provide opinionated go import formatting rules. The linter could:

1. Validate that go import statements are formatted according to the rules listed in x/tools/cmd/goimports: support repairing import grouping/ordering golang/go#20818.
2. In autofix mode, reformat the go import statements according to the opinionated rules.

Issue 20818 is still in ideation stage, but there is already a concrete implementation: https://github.com/rinchsan/gosimports is effectively a drop-in replacement for the goimport command, with additional opinionated rules to group/order go import statements.

Describe the solution you'd like.

I can see two ways to implement this proposal:

1. Introduce a new gosimport linter that uses gosimport instead of goimport.
2. Add a new config attribute to the existing goimports linter. The setting would be used to control which command to use, e.g. goimport or gosimport.

Option 2 seems to be better for users of the golangci-lint tool. There would be one linter to control go import formatting rules, one place to document what the formatting rules are. Also, it seems fairly straightforward to modify https://github.com/golangci/gofmt/tree/master/goimports to support either gosimport or goimport.

Describe alternatives you've considered.

This is a new feature. I'm not aware of the ability to control which go import formatting tool can be used.

Additional context.

Assuming the -local argument is the same for goimport and gosimport:

1. The gosimport command may reformat code that was previously formatted with goimport.
2. The goimport command does not reformat code that was previously formatted with gosimport.

[ldez]

gci already provide this.