feat: support configurable snapshot dir and filename

[gkampitakis]

This pull request adds back support for allowing configurable snapshot filename and directory name. [ pr tha dropped config ]

Action Items:

• Make sure we are backward compatible
• Make sure this doesn't affect the Clean functionality
• Update docs
• Extend unit tests

closes #58

Example usage of current api

t.Run("should allow setting filename", func(t *testing.T) {
    snaps.WithConfig(snaps.Filename("my_custom_name")).MatchSnapshot(t, "Hello Word")
    snaps.WithConfig(snaps.Dir("my_dir")).MatchSnapshot(t, 10, 20, 30)

    snaps.WithConfig(snaps.Filename("my_custom_name")).MatchSnapshot(t, "Hello Word")
    snaps.WithConfig(snaps.Dir("my_dir")).MatchSnapshot(t, 10, 20, 30)

    snaps.WithConfig(snaps.Dir("my_dir"), snaps.Filename("json_file")).MatchJSON(t, `{"hello":"world"}`)
    snaps.WithConfig(snaps.Dir("json_dir"), snaps.Filename("blue_file")).MatchJSON(t, `{"hello":"world"}`)
})