Documentation: Expanding the examples

[shaneutt]

We don't have enough examples in gateway-api/examples. We should add examples here that cover the following:

• Add examples for managing GatewayClass, Gateway, HTTPRoutes and GRPCRoutes to expose a Service #66
• Add examples with more advanced Gateway usage #67
• Add examples for advanced routing with HTTPRoute #68
• Add examples for advanced routing with GRPCRoute #69
• Add examples of building a kube-rs controller with Gateway API #70
• Add examples of building a kubert controller with Gateway API #71

The above list is non-exhaustive, but seems to provide a good baseline.

[shaneutt]

Closing this in favor of the sub-tasks which were spun up for it instead.