MAINTAINERS: configfs: add Andreas Hindborg as maintainer

Remove Joel Becker as maintainer of configfs and add Andreas Hindborg as
maintainer and Breno Leitao as reviewer. Also update the tree URL.

Add an entry for Joel Becker to CREDITS.

Acked-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250326-configfs-maintainer-v1-1-b175189fa27b@kernel.org


Signed-off-by: Christian Brauner <brauner@kernel.org>