Fix docker ignore

[JaewonHur]

This PR fixes container build to use docker specific ignore (#1169).
This PR relies on apple/container-builder-shim#68.

When docker specific ignore file is detected, it creates a hidden docker directory (i.e., .hidden-docker-dir) under the build context, and places Dockerfile and ignore file under there. This hidden directory is passed to the builder shim and used by buildkit daemon to correctly figure out the docker specific ignore file.

Docker specific ignore file is detected regardless of whether i) they are under nested directory, ii) outside build context, iii) using custom names. If docker specific ignore is not provided, hidden directory is also not created, and buildkit daemon will use the docker ignore file at build context root as usual.

Type of Change

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

Motivation and Context

Docker specific ignore works.

Testing

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

[JaewonHur]

╰─❯ TOOL=container ./test-ignore.sh
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Running .dockerignore tests with: container
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[TEST] Test 1: Basic .dockerignore
  $ ( cd test1-basic ; container build -t test-ignore:latest . )
[PASS] included.txt was copied (expected)
[PASS] ignored.txt was NOT copied (expected)

[TEST] Test 2: Dockerfile-specific ignore (Dockerfile.dockerignore)
  $ ( cd test2-specific ; container build -t test-ignore:latest . )
[PASS] specific.txt was NOT copied (correctly ignored by Dockerfile.dockerignore)
[PASS] general.txt was copied (only ignored by .dockerignore, not Dockerfile.dockerignore)

[TEST] Test 3: Containerfile with .containerignore
  $ ( cd test3-containerfile ; container build -f Containerfile -t test-ignore:latest . )
[PASS] included.txt was copied (expected)
[FAIL] ignored.txt was copied (unexpected)

[TEST] Test 4: Containerfile-specific ignore (Containerfile.containerignore)
  $ ( cd test4-containerfile-specific ; container build -f Containerfile -t test-ignore:latest . )
[FAIL] specific.txt was copied (should be ignored by Containerfile.containerignore)
[PASS] general.txt was copied (only ignored by .containerignore, not Containerfile.containerignore)

[TEST] Test 5: Build succeeds when Dockerfile is ignored
  $ ( cd test5-ignored-dockerfile ; container build -f Dockerfile -t test-ignore:latest . )
[PASS] Build succeeded even with Dockerfile in .dockerignore
[PASS] test.txt was copied (expected)

[TEST] Test 6: Build from subdirectory context
  $ ( cd test6-subdir ; container build -f subcontext/Dockerfile -t test-ignore:latest subcontext )
[PASS] included.txt was copied (expected)
[PASS] ignored.txt was NOT copied (expected)

[TEST] Test 7: No ignore file (all files should be copied)
  $ ( cd test7-no-ignore ; container build -t test-ignore:latest . )
[PASS] file1.txt was copied (expected)
[PASS] file2.txt was copied (expected)

[TEST] Test 8: Build with --platform and Dockerfile in subdirectory
  $ ( cd test8-platform-subdir-dockerfile ; container build --platform linux/amd64 -t test-ignore:latest -f nested/project/Dockerfile . )
[PASS] included.txt was copied (Dockerfile.dockerignore takes precedence over .dockerignore)
[PASS] secret.txt was NOT copied (correctly ignored by Dockerfile.dockerignore)
[PASS] nested/project/config.txt was copied (expected)

[TEST] Test 9: Custom-named Dockerfile (app1.Dockerfile)
  $ ( cd test9-custom-dockerfile-name ; container build -f app1.Dockerfile -t test-ignore:latest . )
[PASS] app1-specific.txt was NOT copied (correctly ignored by app1.Dockerfile.dockerignore)
[PASS] generic.txt was copied (only ignored by .dockerignore, not app1.Dockerfile.dockerignore)
[PASS] included.txt was copied (expected)

[TEST] Test 10: Custom-named Dockerfile in subdirectory
  $ ( cd test10-custom-name-subdir ; container build -f nested/project/app2.Dockerfile -t test-ignore:latest . )
[PASS] from-app2-ignore.txt was NOT copied (correctly ignored by app2.Dockerfile.dockerignore)
[PASS] from-root-ignore.txt was copied (only ignored by .dockerignore, not app2.Dockerfile.dockerignore)
[PASS] always-included.txt was copied (expected)
[PASS] nested/project/config.yaml was copied (expected)

[TEST] Test 11: app.Dockerfile with coexisting Dockerfile uses app.Dockerfile.dockerignore not Dockerfile.dockerignore
  $ ( cd test11-coexisting-dockerfiles ; container build -f app.Dockerfile -t test-ignore:latest . )
[PASS] app-specific.txt was NOT copied (correctly ignored by app.Dockerfile.dockerignore)
[PASS] dockerfile-specific.txt was copied (Dockerfile.dockerignore was not used)
[PASS] included.txt was copied (expected)

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Test Summary
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Passed: 25
Failed: 2
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