Configurable timeout for "wait-for-service" for services

Description

I'd like to use services for dependencies, that start rather slowly, but there is no way to do that reliably, if I can't configure the waiting timeout.

context:

Using Docker executor with image docker:18 ...
Starting service docker:18.09-dind ...
Authenticating with credentials from $DOCKER_AUTH_CONFIG
Pulling docker image docker:18.09-dind ...
Using docker image sha256:e4157102c815f9ed8fec6118171866b13a331b6329ff8f85017f0bf7652917e9 for docker:18.09-dind ...
Waiting for services to be up and running...

*** WARNING: Service runner-abc-project-51-concurrent-0-docker-0 probably didn't start properly.

Health check error:
service "runner-abc-project-51-concurrent-0-docker-0-wait-for-service" timeout

in reality, dind starts fast - this is just an example

Proposal

This just an example, what it could look like

job-build:
  services:
    - name: docker:18.09-dind
      alias: docker
      startup_timeout: 60

the wait-for-service would then simply wait for the given amount of time, instead of the system default