Add new amber watch configuration to all recipes

[faustinoaq]

See: amberframework/amber#865

Basically now any developer can customize the amber watch command tasks using .amber.yml file:

type: app
database: sqlite
language: slang
model: granite
watch:
  server:
    files: ["src/**/*.cr", "src/**/*.ecr"]
    command: shards build
  client:
    files: "public/**/*"
    command: ["yarn install", "yarn run watch"]
  jobs:
    files: "src/jobs/*"
    command: crystal run src/sidekiq.cr