feat: Add support to delete by using labels. Depended on by #2116

[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.

Depended on by #2116

This PR is primarily aimed at migrating argo delete to using the apiclient. I present it as a good example of this because:

• I did quite a bit of refactoring of delete.go and it behaves slightly different.
• I added support for --selector as I thought we should not want out tests to delete workflows not labelled with `argo-e2e'. This is a new feature.
• I wrote 4 new e2e tests.
• I actually delete more production code than I wrote.

@whynowy @simster7 @sarabala1979

[codecov]

Codecov Report

Merging #2123 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2123   +/-   ##
=======================================
  Coverage   11.69%   11.69%           
=======================================
  Files          52       52           
  Lines       26353    26353           
=======================================
  Hits         3081     3081           
  Misses      22877    22877           
  Partials      395      395

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[alexec]

@sarabala1979 could I please ask you to review this and other "workflow CLI" PRs?