Change the UI and the auth to support BETA features

[mavishay]

We want to release the application as BETA.
therefore we want to release to a close beta check.

• Disable the (open for all) registration link
• For registration you need to provide a code generated by admin (other members of the applications)
• Change the UI to support the above feature
• Create BE endpoints for creating and validating codes in order to register the application
• Add feature flag in .env that enable/disable this BETA feature