Fix a bug where lfs gc never worked.

[lunny]

Fix #31113

After #22385 introduced LFS GC, it never worked due to a bug in the INI library: fields in structs embedded more than one level deep are not populated from the INI file.

This PR fixes the issue by replacing the multi-level embedded struct with a single-level struct for parsing the cron.gc_lfs configuration.

Added a new test for retrieving cron settings to demonstrate the bug in the INI package.

[wxiaoguang]

But is it right? Is the Test_getCronSettings2 related to the real code?

In the future, if a change in registerGCLFS introduces new bug, the Test_getCronSettings2 still pass and lie to developers that "oh, everything is fine"?

[lunny]

Added a new test for retrieving cron settings to demonstrate the bug in the INI package.

The test just demonstrate there is a bug in the INI package.

[wxiaoguang]

Added a new test for retrieving cron settings to demonstrate the bug in the INI package.

The test just demonstrate there is a bug in the INI package.

Why not provide a correct test for real code?

[lunny]

Added a new test for retrieving cron settings to demonstrate the bug in the INI package.

The test just demonstrate there is a bug in the INI package.

Why not provide a correct test for real code?

17e00d6 added a test for Get GC LFS configuration