fix: split REGISTRY into BUILDER_REGISTRY and REGISTRY

[ESWZY]

Ⅰ. Describe what this PR did

As the documentation says, we can

The registry address of the generated image, e.g. example.registry.io/my-name/. Note that the REGISTRY value should end with /.

But in the Makefile, REGISTRY specifies both the registry of builder and the registry of artifact.

For most users, they may not want to set the builder registry and output image registry to be the same, so it is necessary to separate them.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[CLAassistant]

All committers have signed the CLA.

[johnlanni]

Thanks