Add ImageSpec.from_env

[thomasjpfan]

Tracking issue

Closes flyteorg/flyte#5889

Why are the changes needed?

Resolve notebook environment mismatch described in flyteorg/flyte#5889

What changes were proposed in this pull request?

This PR adds a ImageSpec.from_env into ImageSpec.

How was this patch tested?

I added unit test to this PR and ran this workflow:

from pathlib import Path

from flytekit import current_context, task, workflow, ImageSpec
from flytekit.types.file import FlyteFile

image_spec = ImageSpec.from_env(
    pinned_packages=["joblib"],
    name="myimage",
    registry="localhost:30000",
    packages=[
        "git+https://github.com/thomasjpfan/flytekit@41a6a74df4bab1b7db4f9ff13eb249e94fe7a2e4"
    ],
    apt_packages=["git"],
)


@task(container_image=image_spec)
def create_file() -> FlyteFile:
    working_dir = Path(current_context().working_directory)

    file = working_dir / "outer_file.txt"
    file.write_text("this is some text")

    return file


@workflow
def main() -> FlyteFile:
    return create_file()

[cosmicBboy]

should there be any special handling for when there are overlapping packages in pinned_packages and packages?

e.g. replace the unpinned package with the pinned package and logging via logger.info?

[thomasjpfan]

There is no issue with overlapping unless there is a conflict. For example, this installs flytekit==1.13.8:

uv pip install flytekit flytekit==1.13.8

If there is a conflict, then the builder will error:

uv pip install flytekit==1.13.11 flytekit==1.13.12
  × No solution found when resolving dependencies:
  ╰─▶ Because you require flytekit==1.13.11 and flytekit==1.13.12, we can conclude that your requirements are
      unsatisfiable.

Given that we also have requirements.txt, there can be conflicts there too. I rather have the not do the error checking here.

As an alternative, I considered disallowing packages & requirements here, but it seemed to restrictive.