Support Envoy Proxy deployment metadata configuration

*Description*:
Add the ability to append additional metadata (`metadata.annotations`, `metadata.labels`) to the Deployment resource that Envoy Gateway generates for a Gateway resource.

Currently to attach additional metadata to our Gateway envoy proxy Deployment we use envoyDeployment.patch:
```
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyProxy
metadata:
name: custom-proxy-config-internal
namespace: envoy-gateway-system
spec:
provider:
type: Kubernetes
kubernetes:
envoyDeployment:
patch:
type: StrategicMerge
value:
metadata:
labels:
tags.datadoghq.com/env: prod
tags.datadoghq.com/service: internal-gateway
```

This results in those two additional labels being set on the Deployment:
```
apiVersion: apps/v1
kind: Deployment
metadata:
annotations:
deployment.kubernetes.io/revision: "4"
labels:
app.kubernetes.io/component: proxy
app.kubernetes.io/managed-by: envoy-gateway
app.kubernetes.io/name: envoy
gateway.envoyproxy.io/owning-gateway-name: internal-gateway
gateway.envoyproxy.io/owning-gateway-namespace: envoy-gateway-system
tags.datadoghq.com/env: prod
tags.datadoghq.com/service: internal-gateway
```

It would be nice if we didn't have to use the patch to set these values.

[optional *Relevant Links*:]
- similar functionality to [this issue](https://github.com/envoyproxy/gateway/issues/1626)
- https://github.com/envoyproxy/gateway/blob/2feb1f6f70371133f8c4fabc8e97317c6528a6de/api/v1alpha1/shared_types.go#L86
- https://github.com/envoyproxy/gateway/blob/2feb1f6f70371133f8c4fabc8e97317c6528a6de/api/v1alpha1/shared_types.go#L159
- https://github.com/envoyproxy/gateway/blob/2feb1f6f70371133f8c4fabc8e97317c6528a6de/api/v1alpha1/shared_types.go#L165