chore: bump to go 1.21

[akashsinghal]

Description

What this PR does / why we need it:

bumps all code + pipelines to go 1.21

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 #

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 A
• Test B

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

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (4f58573) 63.14% compared to head (bb037ce) 61.72%.

Files	Patch %	Lines
pkg/policyprovider/policyquery/rego/query.go	40.00%	2 Missing and 1 partial ⚠️
pkg/certificateprovider/azurekeyvault/auth.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1276      +/-   ##
==========================================
- Coverage   63.14%   61.72%   -1.42%     
==========================================
  Files          79       97      +18     
  Lines        5147     6190    +1043     
==========================================
+ Hits         3250     3821     +571     
- Misses       1637     2038     +401     
- Partials      260      331      +71     

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[susanshi]

LGTM. thanks.