Create E2E examples

[Wwwsylvia]

Currently we have several runnable examples for specific APIs. However, we don't have any E2E examples that demonstrates how the APIs can be used together.

[sparr]

Adding some narrative descriptions of example examples here would make it easier for a contributor to implement examples.

[wangxiaoxuan273]

I'd like to work on this.

[Wwwsylvia]

Adding some narrative descriptions of example examples here would make it easier for a contributor to implement examples.

We can migrate the existing quick start examples to the go reference:

1. Push files to a remote repository
2. Pull files from a remote repository
3. Pull a docker or OCI image from a remote repository to a local OCI layout
4. Pull an image using the docker credentials store

And we can also have some examples like:

• Copy an image from an OCI layout tar archive to a remote repository

Please feel free to share any additional examples that you think would be helpful for users.

[Wwwsylvia]

We can also add the links to the new examples in the README: https://github.com/oras-project/oras-go#v2-stable