Sanity checks on dummy configs for integration tests

[RenjieTang]

This issue was discovered in #20259 which used MockClusterInfo for HTTP integration tests.

However the default value of the connect timeout would cause Quiche to complain and crash at QuicConnection::SetNetworkTimeouts.

I think default value like this doesn't make much sense.
I wonder if more of such cases exist in Envoy's integration test setups.

[RyanTheOptimist]

cc: @alyssawilk @danzh2010

[danzh2010]

Thanks for bringing up this issue! I think this is indeed a config sanitization issue rather than test config being non-sense. we need to guard Envoy from bad config input.

[alyssawilk]

+1, we shouldn't accept config which causes ENVOY_BUG later down the line.

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in the next 7 days unless it is tagged "help wanted" or "no stalebot" or other activity occurs. Thank you for your contributions.

[danzh2010]

needs a non-stale tag