[FEATURE] set build context directory

[pfeifferj]

Is your feature request related to a problem? Please describe.

The following scenario seems not to be supported as of yet:

Containerfile + artifacts in a build directory

.
├── build
│   ├── Containerfile
│   └── setup.sh

Containerfile copying artifact from the build directory

(...)
COPY setup.sh .
(...)

The current setup seems to only query the root directory, rather than the build directory:

error building at STEP "COPY setup.sh .": checking on sources under "/home/runner/work/<repo-name>/<repo-name>": copier: stat: "/setup.sh": no such file or directory

Describe the solution you'd like

Add an option to set a build context directory

Describe alternatives you've considered

Additional context

[travier]

This is the push action. You want https://github.com/redhat-actions/buildah-build which has the context option.