convert mfa templates to Twig

[briskt]

Changed

• Converted must-set-up-mfa.php template to Twig
• Converted prompt-for-mfa templates to Twig

Added

• Added .gitkeep files to make templates directories for modules. These will be filled during image creation, but need to exist for local development and test.
• Added .gitkeep files to module locales folders. SSP requires these to exist, but we'll never use the non-themed locales directories.

https://itse.youtrack.cloud/issue/IDP-898

[sonarcloud[bot]]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud