Fix callback-example.yaml

[tfesenko]

The runtime expression must be quoted as it starts with a '{' - an indicator character, otherwise it's invalid YAML.

I also added the 'openapi' and 'info' properties because they are required and, thus, the spec file is invalid without them.

[MikeRalphson]

Was this example ever intended to be complete / self-contained? It also has a missing definition of #/components/schemas/UserLogData

[RobDolinMS]

#TDC: @tfesenko Thank you for submitting this PR. Would you please update per @MikeRalphson's comment so this is a complete example.

You may want to align with what @whitlockjc is drafting for Issue #1245

[whitlockjc]

@tfesenko If you would like to get this addressed ASAP and not wait for #1245, I would just make the following changes to your PR as it will align with our plans:

1. Replaces lines 1-4 with # ... (this will be our way to indicate "omitted for brevity")
2. Resolve the $ref on line 51:
   a. Add # ... as the last line of the document
   b. Replace $ref with an inline schema

I guess 2.a could be documented in #1245 but for now, being explicit might not be a bad thing.

[RobDolinMS]

ACTION: @tedepstein to reach-out to @tfesenko when she's back (likely Mon, 7/10)

[tfesenko]

@whitlockjc , I addressed your suggestions in commit ccf0169. Can you please have a look? Thanks!

[whitlockjc]

[whitlockjc]

Since this is a non-spec change, we should be able to branch/merge into master instead of a release-specific branch. I will have to merge this manually.

[whitlockjc]

Merged manually 542fc44

[whitlockjc]

Weird, it didn't keep your commits but the commit message clearly points to your commit.

[whitlockjc]

@tfesenko I apologize the merged commit didn't retain your authorship of the two commits. I did it this way to avoid asking you to delete this PR and recreate a new one from master. Next time, I'll just ask you to create a new PR so your details in up in the commit log. I apologize.