Add ability to add named imports in a separate group

[ustun-ed]

We have the following internal code style:

• Standard library imports
  • repository imports
  • Vendor imports
  • Named imports (all internal and external named should be in same group)

Example:

import (
    "context"
    "fmt"
    "time"

    "github.com/ourcompany/ourcompany/pkg/log"
    "github.com/ourcompany/ourcompany/pkg/percentile"

        "github.com/google/go-cmp/cmp"

    svc "github.com/ourcompany/ourcompany/pkg/aggregator_service"
)

Could you add support for the final named imports group?

[ustun-ed]

Added a draft PR above.

[incu6us]

@n-oden added it