[android_alarm_manager] Added oneShotAt method to schedule a alarm at a given time

[Afsar-Pasha]

Description

Added a static oneShotAt method to AndroidAlarmManager to run callback at a given DateTime time.

Related Issues

None

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
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Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[bkonyi]

Thanks for the PR! Everything looks good for the most part, just a couple of small adjustments.

[bkonyi]

Thanks for the changes! Looks good to me overall, just one minor style change for approval.

[bkonyi]

Sorry, I missed the formatting error on the last review. If you could just run dartfmt on android_alarm_manager.dart and resubmit, I'll go ahead and merge this. Thanks!

[bkonyi]

Fixes flutter/flutter#27115

[bkonyi]

Published on pub.dev as 0.4.3. Fixes flutter/flutter#37534