feat(artifacts): add new_draft method to modify and log saved artifacts as new version

[szymon-piechowicz-wandb]

Fixes WB-12549

Description

Added the ability to create a new draft artifact bootstrapped with an existing artifact.

Note on API design:
I decided to create a new Artifact instance instead of modifying an existing instance. Changing the identity of an existing instance would be error prone. Note that we keep references to Artifact instances in various places (e.g. here and here) and assume their identity doesn't change over time.

Test plan

[moredatarequired]

How do you feel about making this a method on the artifact being cloned? I.e. draft_artifact = committed_artifact.new_draft() instead of draft_artifact = wandb.Artifact.from_artifact(committed_artifact)? (new_draft might not be the best name, but something along those lines)

[szymon-piechowicz-wandb]

I had it that way at first, and then changed it.

• The advantage of draft_artifact = wandb.Artifact.from_artifact(committed_artifact) is that it's clear you're creating a new instance.
• The advantage of draft_artifact = committed_artifact.new_draft() is that it's more concise.

I don't feel very strongly about this though, I can change it back. What do you think?

[moredatarequired]

I don't feel very strongly about this though, I can change it back. What do you think?

Also no strong opinions. I favor the more concise version. Is there a better name than new_draft() that would make it more obvious you're returning a new instance? What had you called it originally?

I'm happy with whatever you decide you want to go with, I just wanted to bring up the question and make it an explicit decision.

[szymon-piechowicz-wandb]

I thought about artifact.draft() and artifact.new_draft(). The problem with the former is that it looks like it's modifying the state of the artifact in place. The problem with the latter is that it's similar to artifact.new_file() and it might look like it adds some "draft" to the artifact, similar to how artifact.new_file() adds a new file.

Alright, I'll change to artifact.new_draft().

[dmitryduev]

/fix-title