feat: Add name to object metadata

[xprazak2]

I hereby agree to the terms of the CLA available at: https://databend.rs/dev/policies/cla/

Summary

Adds a method to metadata which returns name of the object. Any hints on where it should be used to make clippy happy?

[Xuanwo]

Thanks for the contribution!

Based on our current design, I expect our name() to be:

• End with / if it's a folder, otherwise a file (keep the same behavior with path and id)
• Metadata::name() -> &str and Object::name() -> String (keep the same style with path)

I'm not sure if Path::new() is a good choice for us. Maybe split by / is good enough? (We will consider windows support after #137 with a clear RFC)

I'm open to any ideas, though.

[xprazak2]

Thank you for a review and hints. The trailing slash turns out to be surprisingly tricky as std::path::Path seems to be normalizing them away. Also, when there is a trailing / and I split by it, I cannot add it back and return &str due to ownership, so I return String. Is that ok?

[Xuanwo]

Is that ok?

LGTM, let's go merging this PR! Thanks for your contribution.

[Xuanwo]

Run cargo fmt to make our check happy 😄