CI: Issue to track which CI jobs have been migrated to Buildkite

[DilumAluthge]

1. Packaging (building Julia from source)

• package_freebsd64
• package_linux32
• package_linux64
• package_linuxaarch64
• package_linuxarmv7l
• package_linuxppc64le
• package_macos64
• package_macosaarch64
• package_musl64
• package_win32
• package_win64

2. Testing (running the Julia test suite)

• tester_freebsd64
• tester_linux32
• tester_linux64 (single-threaded)
• tester_linux64 (multi-threaded)
• tester_linux64 (under rr)
• tester_linuxaarch64
• tester_linuxarmv7l
• tester_linuxppc64le
• tester_macos64
• tester_macosaarch64
• tester_musl64
• tester_win32
• tester_win64

3. Miscellaneous

• analyzegc
• doctest
• embedding
• llvmpasses
• sanitizers
• whitespace

4. Scheduled

• coverage
• docdeploy
• package_linux64 (with USE_BINARYBUILDER=0)
• tester_linux64 (with USE_BINARYBUILDER=0)