gnu: kdbusaddons: Embed kinit store dir, avoid dependency cycles.

gnu: kdbusaddons: Embed kinit store dir, avoid dependency cycles.

kdbusaddons needs to know the location of the kdeinit5 executable,
provided by kinit. kinit depends on kdbusaddons, so we add bootstrap
versions of all packages in the dependency chain from kinit to
kdbusaddons to avoid cyclic dependencies.

* gnu/packages/kde-frameworks.scm (kinit-bootstrap,
  kdbusaddons-bootstrap): New variables.
  (kdbusaddons)[inputs]: Add kinit-bootstrap.
  [source,arguments]: Add patch and substitution to embed
  kinit-bootstrap's store directory in the code.
* gnu/packages/patches/kdbusaddons-kinit-file-name.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>