config: change default initial fetch timeout to 15s (#7571)
config: change default initial fetch timeout to 15s (#7571)

Signed-off-by: Rama Chavali <rama.rao@salesforce.com>

Mirrored from https://github.com/envoyproxy/envoy @ 7e7486588239f42b4be3a6383e3c0776d2d05bef

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