Replace e2e test matrix bash script with go-based action

[gjermundgaraba]

Our e2e test matrix is currently generated with a bash script and we have to pass in a string-based list of tests we want to skip.

Instead, we should have a go script that does this, and that can more easily be provided with configuration for which tests to skip. We can also consider pulling this out into a separate repo to make it re-usable for ibc-go (and potentially others who need it)

Ref comment: @srdtrk in #405 (comment)_