add support for raw byte for http response body

[wiyu]

What does this PR do?

Add support to the blackhole to return a raw byte array/vector response. This is to support custom binary types which is used by the datadog process agent.

Testing

1. Baseline
Running the agent with the nothing response from lading shows the process agent logs errors due to the invalid/empty response

  - http:
      binding_addr: "127.0.0.1:9092"
      body_variant: "nothing"

2023-10-16 20:11:43 UTC | PROCESS | ERROR | (pkg/process/runner/runner.go:489 in readResponseStatuses) | [process] Could not decode response body: invalid message length: 0

1. Process Response RT Mode Disabled

  - http:
      binding_addr: "127.0.0.1:9092"
      body_variant: "raw_bytes"
      # process agent RT mode disabled response
      raw_bytes: [0x1, 0x0, 0x17, 0x0, 0xa, 0x2, 0x20, 0x17, 0x1a, 0x2, 0x10, 0xa]

The process agent logs show no errors from the response

2. Process Response RT Mode Enabled

- http:
  binding_addr: "127.0.0.1:9092"
  # process agent RT mode enabled response
  raw_bytes: [0x1, 0x0, 0x17, 0x0, 0xa, 0x2, 0x20, 0x17, 0x1a, 0x4, 0x8, 0x2, 0x10, 0x2]

The process agent logs show RT mode is enabled

2023-10-16 20:36:53 UTC | PROCESS | INFO | (pkg/process/runner/runner.go:229 in logCheckDuration) | Finished process check #2 in 20.911458ms
2023-10-16 20:36:53 UTC | PROCESS | INFO | (pkg/process/runner/runner.go:415 in UpdateRTStatus) | Detected 2 active clients, enabling real-time mode

Motivation

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Related issues

A list of issues either fixed, containing architectural discussions, otherwise relevant
for this Pull Request.

Additional Notes

Anything else we should know when reviewing?

[GeorgeHahn]

This looks great!