Fix code splitting issue

[pettinarip]

With the inclusion of a custom .babelrc (on v4) code splitting stopped working correctly. This is due to a Gatsby bug.

Description

In order to fix it, we have deleted the custom .babelrc (since there seems to be no way of ignoring it from Gatsby) and we have created a custom webpack config file to be used by netlify-lambda.

[gatsby-cloud[bot]]

:white_check_mark: ethereum-org-website-dev deploy preview ready

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[dawsbot]

Is there any perf monitoring on the repo to determine how much this change improved the bundle size?