JMAP Email/set - Update Body Request Format for Specific Header

[vttranlina]

Currently, Tmail support json request with headers: EmailHeader[] under the bodyValues property, structured as follows:

        "htmlBody": [
            {
              "partId": "a49d",
              "type": "text/html"
            }
          ],
          "bodyValues": {
            "a49d": {
              "value": "$htmlBody",
              "isTruncated": false,
              "isEncodingProblem": false,
              "header:Specific:asText": "MATCHME"
            }
          }

However, this format does not comply with RFC8621
The correct format should move the specific header from bodyValues to htmlBody/textBody:

        "htmlBody": [
            {
              "partId": "a49d",
              "type": "text/html",
               "header:Specific:asText": "MATCHME"
            }
          ],
          "bodyValues": {
            "a49d": {
              "value": "$htmlBody",
              "isTruncated": false,
              "isEncodingProblem": false
            }
          }

The James pr apache/james-project#2659 support for both formats. However, the old format is now marked as Deprecated.
We should move to new format

[chibenwa]

Do not work on this too soon: we need backend team to make progress on this first...