feat: fill ErrorReason and Remediation during verifierReport generation

[binbin-li]

Description

What this PR does / why we need it:

1. Update Message and add ErrorReason and Remediation in all returned verifierResult.
2. Add VerifierName and VerifierType fields in verifierResult to replace Name and `Type in next major release.
3. Add unit tests for external plugins.

Example:

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: Patch coverage is 89.06752% with 34 lines in your changes missing coverage. Please review.

Files	Patch %	Lines
...rifier/vulnerabilityreport/vulnerability_report.go	84.07%	32 Missing ⚠️
plugins/verifier/sbom/sbom.go	93.33%	2 Missing ⚠️

Files	Coverage Δ
pkg/executor/core/executor.go	88.46% <100.00%> (-0.70%)	⬇️
pkg/executor/types/types.go	0.00% <ø> (ø)
pkg/policyprovider/configpolicy/configpolicy.go	93.22% <100.00%> (-0.23%)	⬇️
pkg/verifier/cosign/cosign.go	78.67% <100.00%> (+0.12%)	⬆️
pkg/verifier/notation/notation.go	87.09% <100.00%> (-1.03%)	⬇️
pkg/verifier/result.go	100.00% <100.00%> (ø)
pkg/verifier/types/types.go	90.69% <100.00%> (-0.97%)	⬇️
...ugins/verifier/schemavalidator/schema_validator.go	100.00% <100.00%> (+52.08%)	⬆️
plugins/verifier/sbom/sbom.go	97.93% <93.33%> (+32.14%)	⬆️
...rifier/vulnerabilityreport/vulnerability_report.go	88.03% <84.07%> (+0.08%)	⬆️

... and 6 files with indirect coverage changes

[susanshi]

left some questions. thanks @binbin-li .