[Microsoft Exchange Online Message Trace] Use case-insensitive comparison for mailflow direction calculation

[moxarth-rathod]

Proposed commit message

  microsoft_exchange_online_message_trace: Use case-insensitive comparison for mailflow direction calculation

  This change updates the mailflow direction script to compare source.domain and
  destination.domain against configured local domains case-insensitively using
  equalsIgnoreCase. Microsoft Graph can return sender and recipient domains in mixed
  case , so a case-sensitive match previously misclassifies
  internal mail as external.

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

How to test this PR locally

Related issues

• Closes [Microsoft Exchange Online Message Trace]: Lowercase source.domain and destination.domain #19375

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