feat(update): remove create or update

[toumorokoshi]

create or update introduces a new pattern in addition to the existing flow of:

1. getting a resource.
2. if NOT_FOUND, send a create.
3. if found, send an update.

In the future, this could be re-added as an Apply method, which would map to the appropriate REST method of PUT.

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• [x] Enhancement
• [ ] New proposal
• [ ] Migrated from google.aip.dev
• [ ] Chore / Quick Fix

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[rambleraptor]

I'm in favor of this as long as the goal is to add an Apply method. If we don't add Apply long-term, this feels useful.

[toumorokoshi]

Feedback offline from @rofrankel is to wait until apply is merged (issue tracked in #110)

[toumorokoshi]

blocked on #248 - once that is merged, this will also merge.