Trigger build, tag, and publication of porter docker image due to git tagging

[derekpierre]

Type of PR:

• Bugfix
• Feature
• Documentation
• Other

Required reviews:

• 1
• 2
• 3

What this does:

Whenever a git tag is pushed to the repos, trigger a build, tag, and publication of Porter docker image.

Issues fixed/closed:

• Fixes #...

Why it's needed:

Explain how this PR fits in the greater context of the NuCypher Network.
E.g., if this PR addresses a nucypher/productdev issue, let reviewers know!

Notes for reviewers:

What should reviewers focus on?
Is there a particular commit/function/section of your PR that requires more attention from reviewers?

[codecov-commenter]

Codecov Report

Merging #45 (cb92757) into development (f387124) will not change coverage.
Report is 6 commits behind head on development.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##           development      #45   +/-   ##
============================================
  Coverage        87.87%   87.87%           
============================================
  Files               18       18           
  Lines              709      709           
============================================
  Hits               623      623           
  Misses              86       86           

Files	Coverage Δ
porter/__about__.py	100.00% <100.00%> (ø)
porter/fields/taco.py	100.00% <ø> (ø)
porter/interfaces.py	97.43% <100.00%> (ø)
porter/main.py	87.96% <100.00%> (ø)
porter/schema.py	98.64% <100.00%> (ø)