feat: add envelope and encryption-method-name

[tboeckmann]

closes #114 & #115

[todo]

add test for: should error on send if envelope type is empty in the outbound mail

mailchain-web/src/app/services/mailchain/messages/send.service.spec.ts

Lines 123 to 128 in d09afc6

	// TODO add test for: should error on send if envelope type is empty in the outbound mail
	// let outboundMailObject = mailchainTestService.outboundMailObject()
	// outboundMailObject.envelope = ""
	})
	it('should specify encryption-method-name as "aes256cbc" in the outbound mail', () => {

---

This comment was generated by todo based on a TODO comment in d09afc6 in #121. cc @mailchain.

[todo]

add test for: should error on send if encryption-method-name is empty in the outbound mail

mailchain-web/src/app/services/mailchain/messages/send.service.spec.ts

Lines 134 to 139 in d09afc6

	// TODO add test for: should error on send if encryption-method-name is empty in the outbound mail
	// let outboundMailObject = mailchainTestService.outboundMailObject()
	// outboundMailObject["encryption-method-name"] = ""
	})
	})
	});

---

This comment was generated by todo based on a TODO comment in d09afc6 in #121. cc @mailchain.

[tboeckmann]

Example POST from send:

feat: Set envelope on send message #114

{
  "message": {
    "body": "Today was a little rainy in London",
    "headers": {
      "from": "0x92d8f10248c6a3953cc3692a894655ad05d61efb",
      "reply-to": "0x92d8f10248c6a3953cc3692a894655ad05d61efb",
      "to": "0xd5ab4ce3605cd590db609b6b5c8901fdb2ef7fe6"
    },
    "public-key": "0x69d908510e355beb1d5bf2df8129e5b6401e1969891e8016a0b2300739bbb00687055e5924a2fd8dd35f069dc14d8147aa11c1f7e2f271573487e1beeb2be9d0",
    "subject": "Tuesday report"
  },
  "envelope": "0x01",
  "encryption-method-name": "aes256cbc"
}

[robdefeo]

@tboeckmann yes this looks good for this phase. Thanks