To support actions "add" and "remove" against key-pair data fields in update()

[gblpedia]

Currently sdk users have to remain the unchanged part of data in the payload when using update() to overwrite the data field.
Suggest to have actions, add and remove, that users can just add/remove data desirably which need to be changed instead of all of remaining data. Like actions, connect and disconnect to data field, groups.

for example, if users want to add another one key-pair "UAT_MySQL": "The url to the user acceptance testing MySQL database" into the existing data.

"variables": {
    "PROD_MySQL": "The url to the production MySQL database",
    "STG_MySQL": "The url to the staging MySQL database"
}

Users can submit payload below

"variables": {
    "add" : {
       ["UAT_MySQL": "The url to the user acceptance testing MySQL", ...]
   },
   "remove": {
      [...]
   }
}

Currently, users need to submit the payload below to overwrite the variables.

"variables": {
    "PROD_MySQL": "The url to the production MySQL database",
    "STG_MySQL": "The url to the staging MySQL database",
    "UAT_MySQL": "The url to the user acceptance testing MySQL"
}