Add Eslint, Prettier, husky & lint-staged

[drtechie]

• Added Eslint to the project with @angular-eslint/schematics for ensuring JS standards
• Added Prettier for better formatting of code
• Additional configuration so that Prettier is used as an ESLint plugin
• Added scripts in package.json for linting and fixing
• Add husky for pre-commit hooks
• Configure lint-staged to check staged files before committing

[drtechie]

@helenKaryamsetty @devikasuresh20
I have added Eslint and Prettier.

I did not run npm run lint:fix yet.
npm run lint:fix will write all fixes to the file.

Please review this PR and let's discuss the rules for Eslint if any of them needs to be disabled.

cc: @pavangsk @ravishanigarapu

[drtechie]

Adding eslint and prettier

ng add @angular-eslint/schematics
npm install prettier --save-dev
npm install prettier-eslint eslint-config-prettier eslint-plugin-prettier --save-dev

Once eslint and prettier is added, ensure .eslintrc.json is as per this PR (add plugin:prettier).
Add package.json scripts for linting and fixing.

Adding husky and lint-staged

• Husky ensures that hooks are added to git commands.
• lint-staged ensures that only changed files are checked.

npm install husky -D
npm pkg set scripts.prepare="husky install"       
npm run prepare
npx husky add .husky/pre-commit "npx lint-staged"
npm install --save-dev lint-staged

Add "lint-staged" property in package.json to check changed .ts, .css and .HTML files.