[MS365] [Subscriptions] Add Subscriptions data stream

[lucian-ioan]

Proposed commit message

Add Subscriptions data stream.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

Author's Checklist

• [ ]

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Quality Gate failed

Failed conditions
33.7% Coverage on New Code (required ≥ 80%)

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