[container-build]: Support inline Dockerfile from stdin

[saehejkang]

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Motivation and Context

Closes #727

Tested variations of commands with stdin below

echo -e "FROM alpine\nRUN echo 'Hello World'" | container build -t myimage -f - .

container build -t myimage -f - . <<'EOF'
FROM alpine
RUN echo 'Hello World'
EOF

echo -e "FROM alpine\nRUN echo 'Hello World'" > Dockerfile.tmp
container build -t myimage -f Dockerfile.tmp .
rm Dockerfile.tmp

Testing

• Tested locally
• Added/updated tests
• Added/updated docs

[jglogan]

Looks good to me.

Could you add a test for this? Just copy one of the simple tests in CLIBuilderTest and supply the Dockerfile via stdin instead of a file.

I think this will require creating a separate helper function to https://github.com/apple/container/blob/main/Tests/CLITests/Subcommands/Build/CLIBuildBase.swift#L112, since there's nothing in that test support stuff that knows how to pipe stdin into container build.

[saehejkang]

We need to make changes in the run function of the CLITest file as well. There needs to be a way to add the data to the stdin pipe.