Feature/search after before on (#9219)

* initial implementation of after, before, on search flags allowing to restrict the search to a specific day or a date range

* missed setting beforeDate in SearchParams in one place

* fixed condition when only flags are used for search without any plain terms

* changed date format used for after/before/on flags to be in ISO8601 format as suggested in PR comments, added a helper function to pad month and day with zeroes allowing the user user either format, with or without leading zeroes

* corrected expected compare to date setting for the TestParseDateFilterToTimeISO8601 test

* fixed a bug for the scenario when you only have the date flags without any terms, added a couple of tests for that scenario

* updated the date filter logic to use parameters to construct the query instead of simply appending strings together, as suggested in the pull request comments

* added search unit test using date flags

* added a helper function to create a test post with a createat date manually set, updated the test for search using date flags to create test posts with different createat dates to be able to better test the functionality

* MM-11817 Add support for after/before/on search flags with Elasticsearch

* add support to search posts to perform the search in context of the client's timezone when filtering by createat date using on: after: before: flags

* updated tests to match the new signature

api4/post.go

@@ -333,17 +333,23 @@ func searchPosts(c *Context, w http.ResponseWriter, r *http.Request) {
 	includeDeletedChannels := r.URL.Query().Get("include_deleted_channels") == "true"
 
 	props := model.StringInterfaceFromJson(r.Body)
+
 	terms, ok := props["terms"].(string)
 	if !ok || len(terms) == 0 {
 		c.SetInvalidParam("terms")
 		return
 	}
 
+	timeZoneOffset, ok := props["time_zone_offset"].(float64)
+	if !ok {
+		timeZoneOffset = 0
+	}
+
 	isOrSearch, _ := props["is_or_search"].(bool)
 
 	startTime := time.Now()
 
-	results, err := c.App.SearchPostsInTeam(terms, c.Session.UserId, c.Params.TeamId, isOrSearch, includeDeletedChannels)
+	results, err := c.App.SearchPostsInTeam(terms, c.Session.UserId, c.Params.TeamId, isOrSearch, includeDeletedChannels, int(timeZoneOffset))
 
 	elapsedTime := float64(time.Since(startTime)) / float64(time.Second)
 	metrics := c.App.Metrics