fix typo in Agent build status badge

[johnsonshih]

What this PR does / why we need it:
There is a typo in the README.md that causes broken link for Agent build. Correct the typo to show correct link to Agent buildy.

the event type is wrong for Agent and Controller build badge, change to use correct event type to show correct result in badge.
Special notes for your reviewer:

If applicable:

• this PR has an associated PR with documentation in akri-docs
• this PR contains unit tests
• added code adheres to standard Rust formatting (cargo fmt)
• code builds properly (cargo build)
• code is free of common mistakes (cargo clippy)
• all Akri tests succeed (cargo test)
• inline documentation builds (cargo doc)
• all commits pass the DCO bot check by being signed off -- see the failing DCO check for instructions on how to retroactively sign commits