Use pinned eslint version (#6968)

* pin eslint version

* use subdir instead

* move eslint

src/backend/.eslintrc.yml

@@ -0,0 +1,27 @@
+env:
+  commonjs: false
+  browser: true
+  es2021: true
+  jquery: true
+extends:
+  - eslint:recommended
+parserOptions:
+  ecmaVersion: 12
+rules:
+  no-var: off
+  guard-for-in: off
+  no-trailing-spaces: off
+  camelcase: off
+  padded-blocks: off
+  prefer-const: off
+  max-len: off
+  require-jsdoc: off
+  valid-jsdoc: off
+  no-multiple-empty-lines: off
+  comma-dangle: off
+  no-unused-vars: off
+  no-useless-escape: off
+  prefer-spread: off
+  indent:
+    - error
+    - 4