chore: refactor Err msg in notation verifier

[junczhu]

Description

What this PR does / why we need it:

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) *:

Update Error Handling in notation verifier.
Should be reviewed after following PRs get merged:

#1758
#1730

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

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

• CI

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: Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/verifier/notation/notation.go	84.61%	1 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
pkg/verifier/notation/certstoresbytype.go	92.59% <100.00%> (ø)
pkg/verifier/notation/pluginmanager.go	71.42% <100.00%> (ø)
pkg/verifier/notation/notation.go	98.07% <84.61%> (+6.67%)	⬆️

... and 1 file with indirect coverage changes