chore: update codecov config

[junczhu]

Description

What this PR does / why we need it:

Introduced codecov.yaml for code coverage report configuration
Excluded path ./api
REF:
https://app.codecov.io/gh/deislabs/ratify/pull/1237/tree?search=&displayType=tree
https://docs.codecov.com/docs/ignoring-paths

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

All modified and coverable lines are covered by tests ✅

Comparison is base (759f299) 55.40% compared to head (51f1159) 61.41%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1237      +/-   ##
==========================================
+ Coverage   55.40%   61.41%   +6.00%     
==========================================
  Files         105       97       -8     
  Lines        6916     6183     -733     
==========================================
- Hits         3832     3797      -35     
+ Misses       2749     2053     -696     
+ Partials      335      333       -2     

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[akashsinghal]

Curious, what's motivation for adding this?

[binbin-li]

Curious, what's motivation for adding this?

Since api is for CRD generation, and most of them are auto-generated without tests, probably excluding it from test coverage makes sense.