DP-64: Add meta descriptions to each page in the operation guide.

[Bonrob2]

Added description tags for events, alarms, notifications, and business service monitoring sections.

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External References

• Jira (Issue Tracker): https://opennms.atlassian.net/browse/DP-64

The base branch was changed.

[Bonrob2]

@mmahacek , realized I had the wrong target branch, so updated, but after you approved.

[mmahacek]

LGTM