[envoy] Update the internal workspace file to include toolchains (#14328)

The Envoy fuzzers are currently broken with the following error:
```
ERROR: [0m/root/.cache/bazel/_bazel_root/4e9824db8e7d11820cfa25090ed4ed10/external/rules_fuzzing/fuzzing/tools/BUILD:32:10: While resolving toolchains for target @@rules_fuzzing//fuzzing/tools:make_corpus_dir (a2cc2bf): invalid registered toolchain '@envoy//bazel/rbe/toolchains/configs/linux/clang/config:cc-toolchain-arm64': error loading package 'bazel/rbe/toolchains/configs/linux/clang/config': Unable to find package for @@envoy_repo//:containers.bzl: The repository '@@envoy_repo' could not be resolved: Repository '@@envoy_repo' is not defined.
```

This update is inspired by the changes in
envoyproxy/envoy@c175fac.

Author: adisuissa

projects/envoy/WORKSPACE

@@ -27,3 +27,11 @@ envoy_python_dependencies()
 load("//bazel:dependency_imports.bzl", "envoy_dependency_imports")
 
 envoy_dependency_imports()
+
+load("//bazel:repo.bzl", "envoy_repo")
+
+envoy_repo()
+
+load("//bazel:toolchains.bzl", "envoy_toolchains")
+
+envoy_toolchains()