v0.5.0-rc2

API versions: v1beta1, v1alpha2

We expect this to be our final release candidate before launching v0.5.0. This
release candidate includes a variety of cleanup and documentation updates.

Webhook

• Adds webhook validation to ensure that no HTTP header or query param is
  matched more than once in a given route rule. (#1230, @skriss)

Documentation

• Add examples and documentation for v1beta1 (#1238, @EmilyShepherd)
• Add policy attachment example (#1233, @keithmattix)
• Add warning headers for experimental resources/concepts (#1234, @keithmattix)
• All Enum API fields have had updates to clarify that we may add values at any
  time, and that implementations must handle unknown Enum values. (#1258,
  @youngnick)
• Spacing has been improved around the documentation of feature-level
  core/extended support for better readability and clarity. (#1241, @acnodal-tc)
• Update ReferenceGrant docs to include Gateways that reference a Secret in a
  different namespace (#1181, @nathancoleman)

Cleanup

• ReferencePolicyList Items is an array of ReferencePolicy again (#1239,
  @dprotaso)
• This release of experimental-install.yaml will apply successfully. Previous
  releases had some extraneous yaml. (#1232, @acnodal-tc)
• The NamedAddress type is back to support backwards compatibility but it is
  still formally deprecated. (#1252, @robscott)