Support proto as persistent worker protocol

[lamcw]

Currently all swift actions running as persistent workers expect the worker to receive WorkRequest as JSON payload.

rules_swift/swift/internal/actions.bzl

Line 203 in 646d6d2

execution_requirements["requires-worker-protocol"] = "json"

This is however unsupported in certain remote execution service providers, such as EngFlow. The remote spawns in such environments will have requires-worker-protocol ignored even if it is supplied as execution requirements and hence, the worker will fail with

what():  [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: '�'

upon reading the first line of the WorkRequest since a proto payload is being sent instead.

This issue is therefore a feature request to support proto as worker protocol.