Add annotation to configure ingress weight

[Aluxima]

Adding an yggdrasil.uswitch.com/weight annotation would be useful to configure lbEndpoint load_balancing_weight for each ingress.
Omitting it empty would not change the current behavior.

In addition to that, giving a weight of 0 could be a special case to remove an ingress from an Envoy cluster.

[Joseph-Irving]

+1 to this idea, we've discussed in the past having a way to remove an ingress would be nice, as just deleting the ingress causes momentary errors as envoy will still send requests there for a little while.

[Solvik]

and here's the MR #83 !