Refactor (#174)

- Goal was to simplify main.go complexity
- Use common structures and interfaces for all vpn providers
- Moved files around
- Removed some alias models

internal/params/surfshark.go

@@ -1,15 +1,12 @@
 package params
 
 import (
-	"strings"
-
 	"github.com/qdm12/private-internet-access-docker/internal/constants"
-	"github.com/qdm12/private-internet-access-docker/internal/models"
 )
 
 // GetSurfsharkRegion obtains the region for the Surfshark server from the
 // environment variable REGION
-func (r *reader) GetSurfsharkRegion() (region models.SurfsharkRegion, err error) {
+func (r *reader) GetSurfsharkRegion() (region string, err error) {
 	s, err := r.envParams.GetValueIfInside("REGION", constants.SurfsharkRegionChoices())
-	return models.SurfsharkRegion(strings.ToLower(s)), err
+	return s, err
 }