[Outlook] (on-send) Improve Smart Alerts note

[samantharamon]

Also updates image format.

[learn-build-service-prod]

Learn Build status updates of commit fae6009:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/images/block-on-send-subject-cc-infobar.png	✅Succeeded	View
docs/images/block-on-send-subject-cc-inforbar.png	✅Succeeded	n/a (file deleted or renamed)
docs/outlook/outlook-on-send-addins.md	✅Succeeded	View

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[learn-build-service-prod]

Learn Build status updates of commit bef3250:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/images/block-on-send-subject-cc-infobar.png	✅Succeeded	View
docs/images/block-on-send-subject-cc-inforbar.png	✅Succeeded	n/a (file deleted or renamed)
docs/outlook/outlook-on-send-addins.md	✅Succeeded	View

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[learn-build-service-prod]

Learn Build status updates of commit 37307c4:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/images/block-on-send-subject-cc-infobar.png	✅Succeeded	View
docs/images/block-on-send-subject-cc-inforbar.png	✅Succeeded	n/a (file deleted or renamed)
docs/outlook/onmessagesend-onappointmentsend-events.md	✅Succeeded	View
docs/outlook/outlook-on-send-addins.md	✅Succeeded	View

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[learn-build-service-prod]

Learn Build status updates of commit d5d8c11:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/images/block-on-send-subject-cc-infobar.png	✅Succeeded	View
docs/images/block-on-send-subject-cc-inforbar.png	✅Succeeded	n/a (file deleted or renamed)
docs/outlook/onmessagesend-onappointmentsend-events.md	✅Succeeded	View
docs/outlook/outlook-on-send-addins.md	✅Succeeded	View

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