[SPARK-57327][INFRA] Move scheduled CIs for 4.1 to branch-4.1

[gaogaotiantian]

What changes were proposed in this pull request?

Add a unified entry for all scheduled CIs for branch-4.1 (branch41_scheduler.yml). It uses gh workflow to trigger the self-contained build workflows on branch-4.1, and removes the per-build build_branch41_*.yml files from master.

This follows the same approach as SPARK-56990 (#56046), which did this for branch-4.x. SPARK-57267 (#56330) already laid the ground on branch-4.1 by making the build workflows self-contained and dispatchable, so this PR only needs to change the master scheduled tasks.

The scheduler triggers the following targets on branch-4.1 (also exposed via workflow_dispatch): build_java17, build_java21, build_maven, build_maven_java21, build_non_ansi, build_python_3.11, build_python_3.14, build_python_pypy3.10. Note this differs from the branch-4.x set: there is no java25 build on branch-4.1, and branch-4.1 additionally has a pypy3.10 build. The cron times are spread out and chosen to avoid the hours already used by the branch-4.x scheduler.

README.md is updated so the branch-4.1 badges point at the self-contained workflows filtered by ?branch=branch-4.1.

Why are the changes needed?

This is part of decoupling our CIs. All branch-4.1 related CIs should only rely on files on branch-4.1, with the exception of this new scheduler file which is needed on master to trigger scheduled tasks (scheduled workflows only fire from the default branch).

Does this PR introduce any user-facing change?

No. CI only.

How was this patch tested?

These workflows can be triggered manually via workflow_dispatch once merged.

Was this patch authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Claude Opus 4.8)

[gaogaotiantian]

Merged to master.