feat: upgrade go to 1.20 to use coverage profiling for integration tests.

[binbin-li]

Description

What this PR does / why we need it:

Upgrade go version to 1.20 to leverage coverage profiling support for integration tests.
This PR doesn’t make a big difference in the test coverage, but it adds 600 more lines to the reports.

Which issue(s) this PR fixes (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged):

Fixes #791

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Helm Chart Change (any edit/addition/update that is necessary for changes merged to the main branch)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

Test coverage breakdown in main branch:

Test coverage breakdown in this PR:

Checklist:

• Does the affected code have corresponding tests?
• Are the changes documented, not just with inline documentation, but also with conceptual documentation such as an overview of a new feature, or task-based documentation like a tutorial? Consider if this change should be announced on your project blog.
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have appropriate license header?

Post Merge Requirements

• MAINTAINERS: manually trigger the "Publish Package" workflow after merging any PR that indicates Helm Chart Change

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +1.09 🎉

Comparison is base (86a6789) 53.57% compared to head (ded7042) 54.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #833      +/-   ##
==========================================
+ Coverage   53.57%   54.66%   +1.09%     
==========================================
  Files          62       79      +17     
  Lines        3679     4615     +936     
==========================================
+ Hits         1971     2523     +552     
- Misses       1500     1815     +315     
- Partials      208      277      +69     

see 37 files with indirect coverage changes

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[akashsinghal]

Thanks for taking care of this. I think we need to update the dockerfile image builder version here? https://github.com/deislabs/ratify/blob/86a67891fc1a2ffeb343b6e8d514ecd032499f2e/httpserver/Dockerfile#L2