Add set-default-label function

[yuwenma]

This PR adds a new set-default-labels function, based on the set-label transformer. It adds the recommended labels to follow the kpt label conventions.

Right now we only add app-name label, which uses the value from the root Kptfile name. This convention believes that all KRM resources under the same kpt package should be served for a specific application.

An application (or KPT package) can be composed by other applications (nested sub KPT packages).
So the function can accept multiple Kptfile and use the root Kptfile to set the app name.

[yuwenma]

@mengqiy Thank you! Ready for another look.

[mengqiy]

It seems you checked in a binary: scripts/patch_reader/patch_reader.
Please revert it.

[yuwenma]

This PR is waiting for some user message improvements from its dependent set-labels module.

• https://github.com/GoogleContainerTools/kpt-functions-catalog/pull/886/files detect and notice users if no input resources are found.
• fix: set-labels handle slice, change log #892 simplifies the result to only show a summary rather than show each resource's changes.

[yuwenma]

It seems you checked in a binary: scripts/patch_reader/patch_reader. Please revert it.

😆 my local branch has a different name (I rarely use different branch names) and obviously I forgot that after working on other stuff.