adds a `_requires_` key for `ConfigComponent`

[wyli]

Is your feature request related to a problem? Please describe.
ConfigComponent may require another config section to run beforehand, this could be denoted by

comp:
    _target_: monai.module
    _requires_: @another_section_name

[Nic-Ma]

Hi @wyli ,

Could you please help add / mark this ticket to #3482 ? Then we can track all the feature related tasks in #3482.

Thanks.

[wyli]

not sure if I understand it correctly, I updated #3482 to-do list with a link to this ticket.