[Issue] Set default indexer mode to 'schedule'

[m2-assistant]

This issue is automatically created based on existing pull request: #36347: Set default indexer mode to 'schedule'

Description

It is recommended that indexers be in the schedule ("Update by Schedule") mode, and not realtime ("Update on Save") mode. However, when Magento is installed for the first time, all indexers are by default in the "wrong" mode. This pull request changes the default for new indexers to be in the expected / recommended mode.

This change will not impact any existing indexers and therefore existing websites should not notice any impact from this change. If a module with an indexer is installed on an existing website, it will be created with the new default mode: {{{}schedule{}}}.

Manual testing scenarios

1. Install Magento anew
2. Navigate in the admin to System -> Tools -> Index Management
3. Notice the colour of the "Mode" column. Before this change, these were all red, indicating an error/problem; after this change these are all green, indicating that all is well.

[github-jira-sync-bot]

Unfortunately, not enough information was provided to create a Jira ticket. Please make sure you added the following label(s): Reproduced on 2.4.x, ^Area:.*

Once all required labels are present, please add Issue: Confirmed label again.

[github-jira-sync-bot]

✅ Jira issue https://jira.corp.adobe.com/browse/AC-6975 is successfully created for this GitHub issue.

[m2-assistant]

✅ Confirmed by @engcom-Lima. Thank you for verifying the issue.
Issue Available: @engcom-Lima, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.