docs: add WorkloadRef to Rollout spec

[danielhelfand]

Closes #2018

Adds WorkloadRef to Rollout spec documentation. While this closes the issue above, another issue should be opened to see if the Rollout spec docs are fully up to date.

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've signed my commits with DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My builds are green. Try syncing with master if they are not.
• My organization is added to USERS.md.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
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No Coverage information
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[codecov]

Codecov Report

Merging #2019 (bee6710) into master (b115ea8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2019   +/-   ##
=======================================
  Coverage   82.50%   82.50%           
=======================================
  Files         120      120           
  Lines       17054    17054           
=======================================
  Hits        14070    14070           
  Misses       2283     2283           
  Partials      701      701           

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