Fix MR Selection, Go Code Refactor (#358)

refactor: Refactors the Go codebase into a more modular and idiomatic approach
fix: require selection of specific MR when there are multiple targets for a given source branch
feat: Allows for the passing of Gitlab's filter options when choosing an MR, improves MR selection
feat: API to choose an MR from a list based on the provided username's involvement as an assignee/reviewer/author

This is a #MINOR release

lua/gitlab/server.lua

@@ -20,8 +20,11 @@ M.start = function(callback)
     debug = state.settings.debug,
     log_path = state.settings.log_path,
     connection_settings = state.settings.connection_settings,
+    chosen_target_branch = state.chosen_target_branch,
   }
 
+  state.chosen_target_branch = nil -- Do not let this interfere with subsequent reviewer.open() calls
+
   local settings = vim.json.encode(go_server_settings)
   local command = string.format("%s '%s'", state.settings.bin, settings)
 
@@ -117,7 +120,7 @@ M.shutdown = function(cb)
   end)
 end
 
--- Restarts the Go server and clears out all gitlab.nvim state
+---Restarts the Go server and clears out all gitlab.nvim state
 M.restart = function(cb)
   if not state.go_server_running then
     vim.notify("The gitlab.nvim server is not running", vim.log.levels.ERROR)