feat: goimports local prefix

[rfwatson]

Description

Add goimports local-prefix configuration. Fixes #1098.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Version of Go used when building/testing:

• 1.22
• 1.23

How Has This Been Tested?

Mostly manual testing. It seems that testing the actual formatter call could be a bit tricky, happy to take a look at adding some if you think it's worth it though.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[LandonTClipp]

Looks great, let's just extend this a bit more.

[LandonTClipp]

This should be *FormatterOptions so that the yaml map can be nil.

[rfwatson]

Wouldn't we just end up with a zero value FormatterOptions in that case? I was thinking to do it this way to avoid the nil checks later, might be missing something though.

[LandonTClipp]

The reason is pretty complicated. It has to do with the migrate command when going from v2 to v3. If you set the default in koanf then mockery will never have nil values for it.

[LandonTClipp]

This is good but I think people also want to be able to modify the imports.Options struct. I think we can do a functional option style of thing. I suggest something like this:

type FormatterOptions struct {
	GoImports *GoImports
}

type GoImports struct {
	LocalPrefix *string ...
    TabWidth *int ...
}

func (g GoImports) Options() imports.Options {
    return imports.Options{
      TabWidth: g.TabWidth,
      // etc
    }
}

Then:

func goimports(src []byte, opt GoImports) ([]byte, error) {
    imports.LocalPrefix = opt.LocalPrefix
    formatted, err := imports.Process("/", src, opt.Options())

We'd want to set default values in here: https://github.com/rfwatson/mockery/blob/dc7ca2f8c944d58757e85aef489fee65a5da13fd/config/config.go#L68-L85