rest-api: make request timeout configurable (#4006)
rest-api: make request timeout configurable (#4006)

The existing RestApiFetcher implementation used a hard-coded request
timeout of 1s which wouldn't suit all environments. This commit enables
the configuration of request timeout in the RestApiFetcher.

Signed-off-by: Venil Noronha <veniln@vmware.com>

Mirrored from https://github.com/envoyproxy/envoy @ a3364380ae8dbfac692977f3d5a846b7498eb4ba

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