Move AwsToAwsBaseOperator fallback out of init

[fat-catTW]

Move AwsToAwsBaseOperator destination connection fallback out of constructor logic so template fields are assigned verbatim during __init__.

Remove the fixed class from the operator-init exemption list and add regression coverage for default and explicit destination connection behavior.

related: #70296

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[github-actions]

Backport failed to create: v3-3-test. View the failure log Run details

Note: As of Merging PRs targeted for Airflow 3.X
the committer who merges the PR is responsible for backporting the PRs that are bug fixes (generally speaking) to the maintenance branches.

In matter of doubt please ask in #release-management Slack channel.

Status	Branch	Result
❌	v3-3-test

You can attempt to backport this manually by running:

cherry_picker 908115a v3-3-test

This should apply the commit to the v3-3-test branch and leave the commit in conflict state marking
the files that need manual conflict resolution.

After you have resolved the conflicts, you can continue the backport process by running:

cherry_picker --continue

If you don't have cherry-picker installed, see the installation guide.