fix(docker): restore semver build; correct names; simplify build pipeline

[placer14]

This PR includes fixes to further support the automatic deployment pipeline work. Specifically:

• Simplify docker build pipeline and scripts (remove GIT_BRANCH case; isolate workflow commands)
• Fix docker image name (remove extraneous -dev on image name)
• Restore semver publishing behavior (trigger was removed in prior PR)
• Fix semver dev image labeled as production
• Fix step names to be understandable in CircleCI UI

Proof of work:
These images were actually pushed to docker hub if you'd like to test them out:
Dev builds have bin/bash shell for entrypoint: docker run -it --rm --entrypoint=/bin/bash filecoin/sentinel-visor:v0.0.0-rc0-dev
Prod builds have bin/sh shell for entrypoint: docker run -it --rm --entrypoint=/bin/sh filecoin/sentinel-visor:v0.0.0-rc0

• Example build against master: https://app.circleci.com/pipelines/github/filecoin-project/sentinel-visor/1407/workflows/e91e38a0-02a6-4d24-977c-c3f388541ad1/jobs/2892
• Example build aginst tag v0.0.0-rc0: https://app.circleci.com/pipelines/github/filecoin-project/sentinel-visor/1411/workflows/9014200a-8828-431f-8709-cf04e2eb93a3/jobs/2899

[codecov-io]

Codecov Report

Merging #393 (9a59ac4) into master (625a7cc) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #393   +/-   ##
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  Coverage    46.4%   46.4%           
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  Files          24      24           
  Lines        1796    1796           
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  Hits          835     835           
  Misses        834     834           
  Partials      127     127