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/provider/common/portforward.go

@@ -1,5 +0,0 @@
-package common
-
-import "errors"
-
-var ErrPortForwardNotSupported = errors.New("port forwarding not supported")

internal/provider/common/updater.go

@@ -10,10 +10,8 @@ import (
 )
 
 var (
-	ErrNotEnoughServers     = errors.New("not enough servers found")
-	ErrHTTPStatusCodeNotOK  = errors.New("HTTP status code not OK")
-	ErrIPFetcherUnsupported = errors.New("IP fetcher not supported")
-	ErrCredentialsMissing   = errors.New("credentials missing")
+	ErrNotEnoughServers   = errors.New("not enough servers found")
+	ErrCredentialsMissing = errors.New("credentials are missing")
 )
 
 type Fetcher interface {