add phone verification to signup page

[k-boiko]

The result is yet unclear, but options are:

• either to add input for phone number on the first anketa page (along with name, surname, and date of birth) and send verification SMS with OTP code during navigation to next anketa step
• or to make this functionality at once on the main anketa page, where currently is phone number input, and add button to send verification and input for the OTP code nearby

In any way there must be added rate limiting for such request on the backend or the captcha should be added