chore: add dependencies

Author: felixfbecker

package.json

@@ -1,6 +1,9 @@
 {
   "private": true,
   "devDependencies": {
+    "@sourcegraph/eslint-config": "^0.20.19",
+    "@sourcegraph/prettierrc": "^3.0.3",
+    "@sourcegraph/tsconfig": "^4.0.1",
     "eslint": "^7.18.0",
     "husky": "^4.3.8",
     "prettier": "^2.2.1",