Use CryptoRandomBytes instead of CryptoRandomString (#18439)

- Switch to use `CryptoRandomBytes` instead of `CryptoRandomString`, OAuth's secrets are copied pasted and don't need to avoid dubious characters etc.
- `CryptoRandomBytes` gives ![2^256 = 1.15 * 10^77](https://render.githubusercontent.com/render/math?math=2^256%20=%201.15%20\cdot%2010^77) `CryptoRandomString` gives ![62^44 = 7.33 * 10^78](https://render.githubusercontent.com/render/math?math=62^44%20=%207.33%20\cdot%2010^78) possible states.
- Add a prefix, such that code scanners can easily grep these in source code.
- 32 Bytes + prefix

modules/secret/secret_test.go

@@ -10,17 +10,6 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestNew(t *testing.T) {
-	result, err := New()
-	assert.NoError(t, err)
-	assert.True(t, len(result) == 44)
-
-	result2, err := New()
-	assert.NoError(t, err)
-	// check if secrets
-	assert.NotEqual(t, result, result2)
-}
-
 func TestEncryptDecrypt(t *testing.T) {
 	var hex string
 	var str string