feat: subscription feature V1

[tejaskh3]

Issue Description

In this issue, we will create APIs one is to collect the users details such as phone number and email address, and make them subscribe and unsubscribe to RDS's notifications.
And send email to one user only as a POC that we can send email.
For the time being we are only collecting the phone numbers, not using them to send notifications.

Expected Behavior

Users should be able to submit their phone numbers and email addresses through the first API, and the data should be successfully stored in the database, and this makes them subscribed to RDS notifications.
Additionally they should have an option to unsubscribe
In the end we should be able to send notification to one user, for the time being the message can be hard coded as well.

Current Behavior

There is no such feature currently

Screenshots

N/A

Reproducibility

• This issue is reproducible
• This issue is not reproducible

Steps to Reproduce

Severity/Priority

• Critical
• High
• Medium
• Low

Additional Information

Checklist

• I have read and followed the project's code of conduct.
• I have searched for similar issues before creating this one.
• I have provided all the necessary information to understand and reproduce the issue.
• I am willing to contribute to the resolution of this issue.