feat: infra/ci: add lotus-test image as CI build step

[nonsense]

This PR is:

1. Adding a lotus-test Docker target to Dockerfile.lotus
2. Build step to produce lotus-test image on commit to master.

We need this, because we are using the --tags=debug lotus binaries as part of the integration tests for Boost -- https://github.com/filecoin-project/boost/blob/main/.circleci/config.yml#L67

Ideally these images should be produced by filecoin-project/lotus build system.

---

TODO:

• create public ECR repository for lotus-test, same as lotus-dev.

[nonsense]

@travisperson provided this PR is accepted, could you help create the repository on the AWS account (same as lotus-dev)?

This will address the failure on build-and-push-image-2.

[jennijuju]

Please update the title according to the PR template!

lotus/.github/pull_request_template.md

Line 15 in d9c7634

- [ ] The PR title is in the form of of `<PR type>: <area>: <change being made>`

[nonsense]

@magik6k @travisperson any chance we can push this forward? It will be handy if we have up-to-date docker images for dependent projects, such as Boost.

We need:

1. public ECR repo for the image
2. merge of this PR so that we start pushing images to the ECR repo

[travisperson]

Yes, I will create the lotus-test repo