add gocritic/ruleguard checks back again, cleanup code. (#13665)

- remove some duplicated code
- reported a bug, separately fixed in #13664
- using strings.ReplaceAll() when needed
- using filepath.ToSlash() use when needed
- remove all non-Go style comments from the codebase

Co-authored-by: Aditya Manthramurthy <donatello@users.noreply.github.com>

internal/config/identity/openid/jwks_test.go

@@ -85,6 +85,7 @@ func TestPublicKey(t *testing.T) {
 		}
 	}
 
+	//nolint:gocritic
 	if key0, ok := keys[0].(*ecdsa.PublicKey); !ok {
 		t.Fatalf("Expected ECDSA key[0], got %T", keys[0])
 	} else if key1, ok := keys[1].(*rsa.PublicKey); !ok {