Update scheduled-pipelines.adoc

[BeFunes]

Description

• Scheduled pipelines should be called "Schedule triggers" and be presented as triggers, not as an entity of their own
• GitHub App pipelines now support Schedule triggers

Checklist of changes that still need to be made:

• when Update steps and images for new project setup page #9577 gets merged, change the base branch of this PR to "main"
• docs/guides/modules/orchestrate/pages/scheduled-pipelines.adoc should include a mention that "Schedule triggers" were previously called "Schedule pipelines"
• I've tried to replace "Scheduled pipelines" with "Schedule triggers" everywhere. But I didn't touch ref headers and liniks. There is a lot of cross-referenced content that uses the scheduled-pipeline name, for example migrate-scheduled-workflows-to-scheduled-pipelines.adoc, get-started-with-scheduled-pipelines etc. It would be great if we could change all of these
• Check that I haven't forgot some stuff
• Can we rename the tab "Scheduled pipelines" into "Schedule triggers" here, and move it under "triggers"?

Reasons

Why did you make these changes? https://circleci.atlassian.net/browse/OB-484, https://circleci.atlassian.net/browse/DOCSS-1899

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