Deprecate Infrastructure category and move its subcategories under Observability

[jen-huang]

Per direction in elastic/integrations#5123 (comment), the recently introduced Infrastructure category is deprecated in favor of Observability. This PR moves all subcategories under Infrastructure to Observability.

As "Monitoring" existed under both categories, I removed monitoring_infrastructure as no integrations are currently using that category anyway (removal from package spec: elastic/package-spec#490).

[elasticmachine]

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• Start Time: 2023-03-15T08:22:01.111+0000

• Duration: 11 min 35 sec

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