[chore] Update MongoDB spans example

[Kielek]

Fixes N/A

Changes

[editorial] Update MongoDB spans example
Remove all attributes not listed in attributes section and adding db.operation.batch.size to the example.

Worth to review with hide whitespaces options.

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• [ ] Change log entry added, according to the guidelines in When to add a changelog entry.
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[Kielek]

@lmolkova, could you please check it, as we discussed part of it in the private channel?

[Kielek]

Duplicates #3322