Summary

This PR is an exact copy of mongodb-js#5, opened here for ease of review. @vkarpov15

This PR adds support for declaring encrypted schemas, as the first step in adding first class support for CSFLE to mongoose. Functionally:

1. A new schema option, encryptionType, has been added. This is required for schemas that are declaring encrypted fields, and it determines whether the schema will be configured for 'csfle' or 'qe'.
2. Keys in schemas can now be configured with an additional encrypt option. This option contains metadata for libmongocrypt to encrypt the field (which will be automatically included in a schemaMap or encryptedFieldsMap). The contents of this document are exactly the same as the fields used to configure a field for csfle or qe, except that bsonType is not required (inferred from the schema type).

This PR also updates all the schema modifiers / cloning methods to account for updating encrypted fields as well.

Examples

Declare an encrypted schema:

const encryptedSchema = new Schema({
  name: { type: String, encrypt: { keyId: '...' } },
  friend: { 
      // nested objects allowed
      name: { type: String, encrypt: { keyId: '...' } },
  },
  // arrays allowed - but becase of how CSFLE/QE encrypted arrays, the arrays are encrypted as a whole
  books: { type: [String], encrypt: { keyId: '...' } }
}, { encryptionType: 'qe' });

Modify / clone encrypted schemas

encryptedSchema.clone();

encryptedSchema.add({ name: String }) // name is no longer encrypted
encryptedSchema.add({ newKey: { type: String, encrypt: { keyId: '...' } }); // new encrypted key added

encryptedSchema.remove('name'); // name no longer in schema at all

encryptedSchema.pick('friends'); // returns a new schema with only one field, `friends`, that is encrypted.

encryptedSchema.omit('friends'); // returns a new schema with all fields except `frields`