feat: upgrade to Go 1.13. Closes #1375

[alexec]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
• The title of the PR is (a) conventional, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234".
• I have written unit and/or e2e tests for my change. PRs without these are unlike to be merged.
• Optional. I've added My organization is added to the README.
• I've signed the CLA and required builds are green.

Closes #1375

• https://blog.liquidbytes.net/2018/09/quick-and-easy-guide-for-migrating-to-go-1-11-modules/

[codecov]

Codecov Report

Merging #2097 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #2097   +/-   ##
======================================
  Coverage    11.7%   11.7%           
======================================
  Files          52      52           
  Lines       26313   26313           
======================================
  Hits         3081    3081           
  Misses      22837   22837           
  Partials      395     395

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[alexmt]

Argo don't need swagger scheme any more ?

[alexec]

we need anther PR for this

[alexmt]

Add one comment about go modules caching.

I've noticed that codegen and swagger were removed. LGTM as long it is intentional and you have a plan to restore/replace it with something else.