bazel: update CMake instructions in EXTERNAL_DEPS.md (#18799)
bazel: update CMake instructions in EXTERNAL_DEPS.md (#18799)

Signed-off-by: James Heppenstall <b5bbf35ef86f9e33b174ee5d64350430b72f86f1@mongodb.com>
envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,lyft/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy