Format and lint go imports with gci

[andrewwdye]

Go imports are formatted inconsistently throughout the flyteorg codebase. In particular, goimports orders imports within a block and optionally breaks them into standard, default, and third party packages, but it does not reformat already broken import blocks. There is a long discussion about this behavior here. As an alternative gci will ensure that go imports are grouped into exactly the sections requested.

This change

• updates make goimports to run gci to format goimports into three sections: standard, default, and flyteorg
• adds gci as a linter for golangci-lint, which is run using make run

For an example of the formatted output of make goimports, see this dry run for flyteplugins

For instance, before:

import (
	"context"
	"testing"

	"github.com/flyteorg/flyte/flyteplugins/go/tasks/pluginmachinery/core"
	"github.com/flyteorg/flyte/flyteplugins/go/tasks/pluginmachinery/core/mocks"
	"gotest.tools/assert"
)

After:

import (
	"context"
	"testing"

	"gotest.tools/assert"

	"github.com/flyteorg/flyte/flyteplugins/go/tasks/pluginmachinery/core"
	"github.com/flyteorg/flyte/flyteplugins/go/tasks/pluginmachinery/core/mocks"
)