feat(EG-433): create user invite api for onboarding users

[zigtan]

This PR adds a new POST /easy-genomics/user/create-user-invite API endpoint for the FE to use when clicking on the Invite Button and supplying the user's email address.

The API expects the CreateUserInvite type with the JSON format:

{
  OrganizationId: string;
  Email: string;
}

The API will:

• check if the supplied OrganizationId exists
• check if the supplied Email belongs to an existing User to determine:
  • If the User is new, then it will create a Cognito User account, and then add a new User record and Organization-User access mapping record.
    • NOTE: The created Cognito User Account's Username field is used for the Easy Genomics User's UserId field.
  • Otherwise if the User is existing, then it the User just needs to be added to the Organization by creating a new Organization-User access mapping record.

The logic checks if such a mapping exists first, and if the Organization-User access mapping record’s status is still Invited to allow for re-sending of invitations.

There is added error handling and cleanup if a User record / Organization-User access mapping record failed to be created for any reason.

The sending of email invitations is not implemented yet, and will be done in a separate ticket to add a reusable email-service.