[BUG] -f option should be resolved relative to the context directory

[tetchel]

ie if you do buildah bud -f Containerfile ./my-buildah-dir then it should look for the containerfile at ./my-buildah-dir/Containerfile

for some reason, absolute paths are used https://github.com/redhat-actions/buildah-build/blob/main/src/index.ts#L61

[tetchel]

this would be a breaking change, so maybe we can leave it as-is for now.

[tetchel]

i'm moving this to 'done' because we don't have a 'wontfix' pipeline.

[evanshortiss]

Just got bitten by this. IIRC other actions use the behaviour described in the Issue description. I opened #123 since it would be helpful to document this behaviour.