fix(sdk): fix kfp component build only produces empty requirements.txt

[chensun]

Description of your changes:

• Collect runtime dependencies specified via packages_to_install, and install them at container build time.
• Rename the system generated requirements.txt to runtime-requirements.txt so that users may keep their requirements.txt which may contain dependencies for the entire project.
• Always update/overwrite runtime-requirements.txt every time users run kfp component build.

Checklist:

• The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

[connor-mccarthy]

/lgtm

This looks great. Thanks, @chensun.

A few thoughts that do not need to block merge:

• Perhaps add a release note, particularly to note the preservation of the user environment requirements.txt file
• Unrelated to this PR: I think it might be good to update the CLI help text (docstrings) to use language that is consistent with our v2 documentation ("Containerized Python Components") here and here. The lack of identical language makes the current text slightly suggestive of CUJ3, particularly on line component.py:334. We can also probably drop the "v2" in the help text. IMO, this is implied by the kfp version the user is using, but I can see other views on this.

[chensun]

/lgtm

This looks great. Thanks, @chensun.

A few thoughts that do not need to block merge:

• Perhaps add a release note, particularly to note the preservation of the user environment requirements.txt file
• Unrelated to this PR: I think it might be good to update the CLI help text (docstrings) to use language that is consistent with our v2 documentation ("Containerized Python Components") here and here. The lack of identical language makes the current text slightly suggestive of CUJ3, particularly on line component.py:334. We can also probably drop the "v2" in the help text. IMO, this is implied by the kfp version the user is using, but I can see other views on this.

All good points! I prepared a release PR that will add the release note for this and some previous PRs.
For the second bullet point, can you help me with the effort?

[chensun]

/approve

[google-oss-prow]

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