Separate module for e2e tests

[seantking]

Background

I think it might be a nice to have to separate the e2e tests into their own module. Some benefits from doing this would be the osmosis binary would be lighter (no longer building the e2e tests) and speed up docker build times when making changes to tests locally.

Suggested Design

Add a go.mod and separate out the e2e tests into their own module.

[seantking]

I can pick this up if it's something useful. Should be light work.