Remove default GatewayParameters from helm API

[timflannagan]

Split out from the #10640 issue. Removing the default GatewayParameter template and it's corresponding values from the chart achieves the following goals:

• Removes multiple APIs for the same CR (helm && GWP)
• Reduces the control plane helm chart values surface in preparation for the first release
• Simplifies the initial setup UX. The default GWP resource is responsible for providing configuration to the deployer component, but after discussion with several maintainers, we feel this current approach could be solved differently

DoD:

• Removal of the GWP template in the chart
• Removal of the top-level gateway values in the control plane chart values
• Handle defaulting via GWP Go type definition

TODO: Hmm... should this be done after the related GC issue?