Groupware improvements: refactoring, k6 tests

* refactored the models to be strongly typed with structs and mapstruct
   to decompose the dynamic parts of the JMAP payloads

 * externalized large JSON strings for tests into .json files under
   testdata/

 * added a couple of fantasy Graph groupware APIs to explore further
   options

 * added k6 scripts to test those graph/me/messages APIs, with a setup
   program to set up users in LDAP, fill their IMAP inbox, activate them
   in Stalwart, cleaning things up, etc...

pkg/jmap/testdata/mailboxes1.json

@@ -0,0 +1,121 @@
+{"methodResponses": [
+	["Mailbox/get", {
+		"accountId":"cs",
+		"state":"n",
+		"list": [
+			{
+				"id":"a",
+				"name":"Inbox",
+				"parentId":null,
+				"role":"inbox",
+				"sortOrder":0,
+				"isSubscribed":true,
+				"totalEmails":10,
+				"unreadEmails":8,
+				"totalThreads":10,
+				"unreadThreads":8,
+				"myRights":{
+					"mayReadItems":true,
+					"mayAddItems":true,
+					"mayRemoveItems":true,
+					"maySetSeen":true,
+					"maySetKeywords":true,
+					"mayCreateChild":true,
+					"mayRename":true,
+					"mayDelete":true,
+					"maySubmit":true
+				}
+			},{
+				"id":"b",
+				"name":"Deleted Items",
+				"parentId":null,
+				"role":"trash",
+				"sortOrder":0,
+				"isSubscribed":true,
+				"totalEmails":20,
+				"unreadEmails":0,
+				"totalThreads":20,
+				"unreadThreads":0,
+				"myRights":{
+					"mayReadItems":true,
+					"mayAddItems":true,
+					"mayRemoveItems":true,
+					"maySetSeen":true,
+					"maySetKeywords":true,
+					"mayCreateChild":true,
+					"mayRename":true,
+					"mayDelete":true,
+					"maySubmit":true
+				}
+			},{
+				"id":"c",
+				"name":"Junk Mail",
+				"parentId":null,
+				"role":"junk",
+				"sortOrder":0,
+				"isSubscribed":true,
+				"totalEmails":0,
+				"unreadEmails":0,
+				"totalThreads":0,
+				"unreadThreads":0,
+				"myRights":{
+					"mayReadItems":true,
+					"mayAddItems":true,
+					"mayRemoveItems":true,
+					"maySetSeen":true,
+					"maySetKeywords":true,
+					"mayCreateChild":true,
+					"mayRename":true,
+					"mayDelete":true,
+					"maySubmit":true
+				}
+			},{
+				"id":"d",
+				"name":"Drafts",
+				"parentId":null,
+				"role":"drafts",
+				"sortOrder":0,
+				"isSubscribed":true,
+				"totalEmails":0,
+				"unreadEmails":0,
+				"totalThreads":0,
+				"unreadThreads":0,
+				"myRights":{
+					"mayReadItems":true,
+					"mayAddItems":true,
+					"mayRemoveItems":true,
+					"maySetSeen":true,
+					"maySetKeywords":true,
+					"mayCreateChild":true,
+					"mayRename":true,
+					"mayDelete":true,
+					"maySubmit":true
+				}
+			},{
+				"id":"e",
+				"name":"Sent Items",
+				"parentId":null,
+				"role":"sent",
+				"sortOrder":0,
+				"isSubscribed":true,
+				"totalEmails":0,
+				"unreadEmails":0,
+				"totalThreads":0,
+				"unreadThreads":0,
+				"myRights":{
+					"mayReadItems":true,
+					"mayAddItems":true,
+					"mayRemoveItems":true,
+					"maySetSeen":true,
+					"maySetKeywords":true,
+					"mayCreateChild":true,
+					"mayRename":true,
+					"mayDelete":true,
+					"maySubmit":true
+				}
+			}
+		],
+		"notFound":[]
+	},"0"]
+], "sessionState":"3e25b2a0"
+}