Support streaming logs for remote builds.

[welteki]

Description

Add support for streaming build logs when building function using the OpenFaaS Function Builder API

Switch to the "github.com/openfaas/go-sdk/builder" package for building functions.

• Use the builder.FunctionBuilder to invoke the Function Builder API for remote builds. Both the faas-cli up and faas-cli publish command stream build logs to sdout if the Function Builder API supports it.

• Switch to using the builder.CreateBuildeContext and builder.MakeTar functions from the Go SDK instead of their local variants.

Motivation and Context

• [ ] I have raised an issue to propose this change (required)

Provide real time feedback on build progress for remote builds.

How Has This Been Tested?

• Verified both the faas-cli up and faas-cli publish command work as expected when using the remoter builder. Verified build logs are streamed in real time when using the latest version of the function builder.

  faas-cli  up --remote-builder http://127.0.0.1:8081 \
    --payload-secret $HOME/.openfaas/payload.txt
  

  faas-cli publish --remote-builder http://127.0.0.1:8081 \
    --payload-secret $HOME/.openfaas/payload.txt
  

• Verified both the faas-cli up and faas-cli publish command still work with older versions (<0.4.3) of the function builder that do not support streaming build logs.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I've read the CONTRIBUTION guide
• [x] I have signed-off my commits with git commit -s
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.