feat: add code linting/formatting configs

.eslintrc.js

@@ -0,0 +1,41 @@
+module.exports = {
+  // https://github.com/newrelic/eslint-plugin-newrelic
+  extends: [
+    'plugin:@newrelic/eslint-plugin-newrelic/react',
+    'plugin:@newrelic/eslint-plugin-newrelic/prettier',
+    'plugin:jsx-a11y/recommended',
+    'plugin:react-hooks/recommended',
+  ],
+  // https://github.com/yannickcr/eslint-plugin-react#configuration
+  plugins: ['react', 'jsx-a11y', 'markdown'],
+  settings: {
+    react: {
+      version: 'detect',
+    },
+  },
+  parserOptions: {
+    ecmaFeatures: {
+      jsx: true,
+    },
+    ecmaVersion: 2018,
+    sourceType: 'module',
+  },
+  env: {
+    browser: true,
+    es6: true,
+  },
+  ignorePatterns: ['**/__tests__/**/*'],
+  rules: {
+    'jsx-a11y/no-onchange': 0,
+    'no-unused-vars': [
+      'error',
+      {
+        vars: 'all',
+        varsIgnorePattern: '^_',
+        args: 'after-used',
+        argsIgnorePattern: '^_',
+        ignoreRestSiblings: false,
+      },
+    ],
+  },
+};

.prettierrc.js

@@ -0,0 +1,9 @@
+module.exports = {
+  trailingComma: 'es5',
+  printWidth: 80,
+  tabWidth: 2,
+  semi: true,
+  singleQuote: true,
+  jsxSingleQuote: false,
+  arrowParens: 'always',
+};