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

cmd/app/config.go

@@ -0,0 +1,23 @@
+package app
+
+type PluginOptions struct {
+	GitlabUrl string `json:"gitlab_url"`
+	Port      int    `json:"port"`
+	AuthToken string `json:"auth_token"`
+	LogPath   string `json:"log_path"`
+	Debug     struct {
+		Request  bool `json:"go_request"`
+		Response bool `json:"go_response"`
+	} `json:"debug"`
+	ChosenTargetBranch *string `json:"chosen_target_branch,omitempty"`
+	ConnectionSettings struct {
+		Insecure bool   `json:"insecure"`
+		Remote   string `json:"remote"`
+	} `json:"connection_settings"`
+}
+
+var pluginOptions PluginOptions
+
+func SetPluginOptions(p PluginOptions) {
+	pluginOptions = p
+}