feat: config file as option (#42)

Fix https://github.com/lampajr/backporting/issues/37

This enhancement required a huge refactoring where all arguments
defaults have been centralized in one single place ArgsParser#parse

src/service/args/args-utils.ts

@@ -0,0 +1,22 @@
+import { Args } from "@bp/service/args/args.types";
+import * as fs from "fs";
+
+/**
+ * Parse the input configuation string as json object and 
+ * return it as Args
+ * @param configFileContent 
+ * @returns {Args}
+ */
+export function parseArgs(configFileContent: string): Args {
+  return JSON.parse(configFileContent) as Args;
+}
+
+/**
+ * Read a configuration file in json format anf parse it as {Args}
+ * @param pathToFile Full path name of the config file, e.g., /tmp/dir/config-file.json
+ * @returns {Args}
+ */
+export function readConfigFile(pathToFile: string): Args {
+  const asString: string = fs.readFileSync(pathToFile, "utf-8");
+  return parseArgs(asString);
+}