Rename pkg.yaml to testdata.yaml

[suzuki-shunsuke]

What

Rename pkgs/**/pkg.yaml to testdata.yaml.

Why

pkg.yaml is just test data.
You can install any versions not listed here.
But the file name pkg.yaml is ambiguous and users misunderstand that only versions listed in pkg.yaml are available.
So I'd like to clarify the meaning of pkg.yaml.
I think the name testdata.yaml is easy to understand the meaning.

Note

We need to fix registry-tool, registry-action, and this repository's scripts too.

• https://github.com/search?q=repo%3Aaquaproj%2Fregistry-tool%20pkg.yaml&type=code
• https://github.com/search?q=repo%3Aaquaproj%2Faqua-registry+pkg.yaml+path%3Ascripts&type=code
• https://github.com/search?q=repo%3Aaquaproj%2Fregistry-action%20pkg.yaml&type=code