Merge branch 'selftests-rds-add-config-file-and-config-sh-c-option'

Allison Henderson says:

====================
selftests: rds: add config file and config.sh -c option

This series adds an RDS-specific config file for ksft CI and extends
config.sh with a -c flag to specify an alternate config file path.
Users can now specify the path of the config they want to update, or
default to .config if none is specified.
====================

Link: https://patch.msgid.link/20260320041834.2761069-1-achender@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>