P4Runtime Release v1.2.0

Second minor release for P4Runtime v1.

Changelog:

• API
  • Add new OPTIONAL match kind. At the moment, OPTIONAL is only supported by the v1model architecture, and not by PSA. It will eventually be included in the core P4 language.
  • Add support in P4Info for structured annotations, which are used to annotate objects with key-value lists or expression lists.
  • Add a new metadata field of type bytes to TableEntry. This is more flexible than the now deprecated controller_metadata field.
  • Add the ability to change the ID of table match fields, action parameters, Packet IO metadata fields, and Value Set match fields in P4Info by using the @id annotation.
  • Support using string as the controller type in the @p4runtime_translation annotation. Update syntax when using a fixed-width unsigned bitstring as the controller type.
  • Add optional P4 source locations to both structured and unstructured annotations.
• specification
  • Clarify the behavior of some corner cases involving action profiles and selectors, including the watch port feature.
• build
  • Overhaul of the Bazel build system
    • Fix rules: remove dependency on stackb/rules_proto, use bazelbuild/rules_proto instead,
    • Improve documentation.
    • Add an example Bazel project depending on the P4Runtime rules.