chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/server/wrappers.go

@@ -1,7 +1,6 @@
 package server
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/qdm12/gluetun/internal/constants"
@@ -12,16 +11,14 @@ type statusWrapper struct {
 	Status string `json:"status"`
 }
 
-var errInvalidStatus = errors.New("invalid status")
-
 func (sw *statusWrapper) getStatus() (status models.LoopStatus, err error) {
 	status = models.LoopStatus(sw.Status)
 	switch status {
 	case constants.Stopped, constants.Running:
 		return status, nil
 	default:
-		return "", fmt.Errorf("%w: %s: possible values are: %s, %s",
-			errInvalidStatus, sw.Status, constants.Stopped, constants.Running)
+		return "", fmt.Errorf("invalid status: %s: possible values are: %s, %s",
+			sw.Status, constants.Stopped, constants.Running)
 	}
 }