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

integrations/api_oauth2_apps_test.go

@@ -43,7 +43,7 @@ func testAPICreateOAuth2Application(t *testing.T) {
 	DecodeJSON(t, resp, &createdApp)
 
 	assert.EqualValues(t, appBody.Name, createdApp.Name)
-	assert.Len(t, createdApp.ClientSecret, 44)
+	assert.Len(t, createdApp.ClientSecret, 56)
 	assert.Len(t, createdApp.ClientID, 36)
 	assert.NotEmpty(t, createdApp.Created)
 	assert.EqualValues(t, appBody.RedirectURIs[0], createdApp.RedirectURIs[0])