[SCRAM] Implement SCRAM register-client flow on the client portal

[interestIngc]

Implement the new register-client flow with a goal to support SCRAM authentication on the client portal.
We have to:

• Fetch the parameters required to generate storedKey and serverKey on frontend, i.e. iterationCount and salt (that can be achieved by creating a new endpoint register-client-precheck on backend to return this data given client username)
• generate saltedPassword, storedKey and serverKey on frontend as per the sequence diagrams
• Send client-specific data (username, backend_uri, redirect_uri, etc) as well as hashes that now represent user's password (i.e. storedKey and serverKey) to the backend
• On the backend, persist this data into the clients table

Acceptance criteria:

1. Put all the changes necessary to implement this functionality under version v2 (i.e. new API endpoints, API endpoint modifications, as well as new methods)
2. The client is successfully able to register using the new flow
3. storedKey and serverKey are persisted into the clients table instead of the password
4. Implementation is fully covered with unit tests

[NJavokhir]

This is sequence diagram for implementing SCRAM Register Client Flow. For more, here is the link
https://excalidraw.com/#room=afd0f1b92250b20f7fc4,3zjNg1wl63K_dHV4mDBpUw