fix: new bundle size esm action

[vasco-santos]

The bundle size action was changed in #865 to support ESM modules, which need > Node@14 but github actions currently only support Node@12 (references in the #865 description).

We are now using Docker, where we need to have dist/index.js in the module to check the bundle size. While this file will always exist on a ESM build via https://github.com/mikeal/ipjs, it might not exist every time on a regular aegir build with CJS like ipfs/js-ipfs-utils#137 and multiformats/js-multiaddr#206 which have their bundle size ci job failing.

The proposal with this PR is to add a new bundle size action for ESM purposes, keeping the previous one without docker. Given we already use this in https://github.com/achingbrain/uint8arrays I am separating this in aegir in 2 PRs, one to add ESM action, then update uint8arrays and finally revert regular action.

This will also mean that CJS running action will be faster as there is no need to have the extra Docker container setup for checking the bundle size.

[vasco-santos]

Close as Solution is in #877