feat(Datastore): add samples for multiple inequality

[bshaffer]

• adds new sample query_filter_compound_multi_ineq
• removes now invalid sample inequality_invalid (see chore: refactor datastore samples #2033)

[snippet-bot]

Here is the summary of changes.

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• datastore/api/src/query_filter_compound_multi_ineq.php:38, tag datastore_query_filter_compound_multi_ineq

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[clairekeer1997]

This is Jia from Firestore Queries team. This PR looks good to me. Thanks for making the change!