Appwrite CLI - Flutter and Generator commands

[lohanidamodar]

What does this PR do?

• Adds a Flutter command and Generate to Appwrite CLI
  • appwrite flutter configure command is used to setup Flutter project, link with appwrite project, add platforms and add and initialize Appwrite SDK
  • appwrite generate <language> is used to generate data classes for all the database collections in the project (Dart, Typescript, Kotlin and Swift implemented, this covers our Client side libraries.)

Test Plan

(Write your test plan here. If you changed any code, please provide us with clear instructions on how you verified your changes work.)

Related PRs and Issues

• demo on https://github.com/appwrite/sdk-for-cli/pull/82

Have you read the Contributing Guidelines on issues?

YES