Add GitHub action for local example

[morgo]

Part of #4989

The local_example test does not require any Python. It is also based on the documentation for contributing Vitess.

This PR creates a GitHub action to install it using the same steps as on the docs: which is nice, because if a dependency sneaks in we will know the website is out of date.

It does not use bootstrap.sh, but a copy of it (what I hope will eventually be the primary bootstrap, but I am having trouble ( #5382 ) getting it to retrofit with the existing CI due to Docker cache. If I disable cache it works.. but tests time out.)

This uses the layout of building from a single directory. It does not require build.env or dev.env to build. It only uses it in bootstrap for the goversion_min function.

Once this merges and is verified as working, we can move local_example to shard 5 (unused) in the CI so it doesn't have to run redundantly.

As more tests are converted to pure-go, we can add them as GitHub Actions. I evaluated CircleCI / Travis / CodeBuild and GitHub actions, and I think this is the best way to move forward.

Note: it uses Go 1.13, which is not a requirement. I compared it to Go 1.12, and it's about 30 seconds faster to download dependencies because I assume it uses a Go module proxy.

Signed-off-by: Morgan Tocker tocker@gmail.com

[deepthi]

This is great! How can we see the result of the github action?

[morgo]

This is great! How can we see the result of the github action?

You can see it where the fork is, so in this case PlanetScale: https://github.com/planetscale/vitess/actions

I really like the way GitHub does it. I saw one mention of limits being 20 actions per repo - so we can have that many .yml files for each of our tests and execute in parallel. Also: if we don't want to do some tests on push but on a schedule, Actions has first class support for that without having to set anything up.

[deepthi]

Nice work! LGTM.