Export CreateBuildContext function from the builder package.

[welteki]

Description

Simplify the signature of createBuildContext and export the function so that it can be used by other packages.

Usage example:

import (
    "log"

    "github.com/openfaas/faas-cli/builder"
    "github.com/openfaas/faas-cli/stack"
)

handler := "./hello-world"
lang := "node20"
fnName := "hello-world"

template, err := stack.LoadLanguageTemplate(handler)
if err != nil {
    log.Fatal(err)
}

buildContext, err := builder.CreateBuildContext(fnName,  handler, template, []string{})
if err != nil {
    log.Fatal(err)
}

Motivation and Context

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

Expose more of the builder functionality for use outside of the faas-cli. This change was primarily made for OpenFaaS users that want to integrate with the Function Builder API and allows them to easily create the function build context from go code.

How Has This Been Tested?

• Verified the faas-cli build and faas-cli publish commands still function as expected for functions using both the dockerfile template and other templates.

• Used the CreateBuildContext function in an updated version of the function builder examples

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.