feat: add build-context support

[0Itsuki0]

Add support for named build contexts, equivalent to Docker/Buildx and Podman --build-context name=value.

Type of Change

• New feature

Motivation and Context

Supporting named build contexts : resolve #1930

Supported formats:

• name=/absolute/or/relative/local/path
• name=docker-image://xxx
• name=oci-layout:/path/to/layout (with or without digest)
• URL/Git

Testing

• Tested locally

1. Check out the container fork for enabling build-context option
2. build the container by running make all && make install
3. Check out builder shim fork
4. build the shim image by running container build -t builder .
5. update build image in container config at ~/.config/container/config.toml

[build]
image = "builder:latest"

6. Use the BuildContextTest.zip to test out all 4 scenarios above + when a regular build where no named context is specified.