Validate referential integrity and logical integrity of datatypes in schema

[aahnik]

The first pr #1 creates endpoints with only basic datatype validation. The admins are expected to enter logically correct data, and the API is expected to be used from an interface only by admins.

For more robust security, we will ship referential integrity constraints and logical integrity constraints in upcoming PRs

for example in the team schema contains MemberRoleD and DomainRoleD types

export class MemberRoleD {
  user: ObjectId; // id of user
  roleStartDate?: Date;
  roleEndDate?: Date;
}

export class DomainRoleD {
  domain: ObjectId; // id of domain
  domainLeads: MemberRoleD[];
  members: MemberRoleD[];
}

in future we must verify:

• whether if user: ObjectId is a valid object id pointing to an user existing in db
• and similarly for domain:ObjectID
• we need to verify whether values of roleStartDate and roleEndDate are within logical bounds, and whether roleEndDate comes after roleStartDate