[MM-20684] Slash Command Autocomplete (#14557)

* [MM-20684] Initial implementation of the Command Autocomplete (#13602)

* Implement Autocomplete Data

* Change CommandName to Trigger

* Fix Autocomplete test

* Make stylistic changes

* Rename a bunch of fields and methods

* Fix variable names, safer type assertions

* [MM-20684] plugin autocomplete implementation (#14259)

* Add an endpoint for command autocomplete suggestions

* Add full Suggestion to the AutocompleteSugestion struct

* Add Dynamic Argument support

* Tidy up things

* Fix missed test case

* Add support of the named arguments

* Update autocomplete API

Fix review issues

Implement dynamic args as a local request

* Fix ineffassign

* Add support of the uppercase letters in arguments

* Add support of the optional arguments

* Remove ineffectual assignment

* Add support for icons (#14489)

* Address couple of nits

* Add comment to IconData

* Add types to all consts

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

plugin/client_rpc.go

@@ -99,6 +99,9 @@ func init() {
 	gob.Register(&model.AppError{})
 	gob.Register(&ErrorString{})
 	gob.Register(&opengraph.OpenGraph{})
+	gob.Register(&model.AutocompleteDynamicListArg{})
+	gob.Register(&model.AutocompleteStaticListArg{})
+	gob.Register(&model.AutocompleteTextArg{})
 }
 
 // These enforce compile time checks to make sure types implement the interface