[License]Add foaas badge in README.md

[B1F030]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:

Which issue(s) this PR fixes:
Part of #5048

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 28.22%. Comparing base (513d90c) to head (e697a9a).

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5050      +/-   ##
==========================================
- Coverage   28.23%   28.22%   -0.01%     
==========================================
  Files         632      632              
  Lines       43434    43434              
==========================================
- Hits        12264    12261       -3     
- Misses      30276    30278       +2     
- Partials      894      895       +1     

Flag	Coverage Δ
unittests	28.22% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[B1F030]

Local preview:

Github preview.

[zhzhuang-zju]

/lgtm
cc @RainbowMango

[RainbowMango]

/approve

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [RainbowMango]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment