tools: improve proto_sync.py UX. (#9699)
tools: improve proto_sync.py UX. (#9699)

Avoid deleting files without prompting, link back to the recommended extension API flow.

Risk level: Low
Testing: Manual

Fixes #9610

Signed-off-by: Harvey Tuch <htuch@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 6ed1df2bdff19ada78f2253f931e68d9343eb398

lyft/envoy-api,lyft/envoy-api,lyft/envoy-api