aws-setup: migrate to flat config

Using npx @eslint/migrate-config .eslintrc.json
Then add the additional packages needed
(@eslint/compat, globals, @eslint/eslintrc, @eslint/js)
Add paths from the .gitignore file to the ignored patterns.
Add .mjs files to the prettier pattern that the eslint.config.mjs is also prettied.
Also lint .ts files with eslint (this seems not to be the default).
Remove the options from the call to eslint which are not
supported anymore in the package.json.

Issue: ecamp#5282