MANIFEST.in: fix package data files missing from rpm

I am certain that the .varlink and .proto files were being added to the
source tarballs and wheels. However, when testing the container image I
found that they were missing from the RPM. After mostly fruitless web
searches and some pretty nonsense LLM responses I closely read the
output being generated by the rpm python tools and revisited the docs
and it managed to loosen something up to revisit MANIFEST.in and...
it worked.

Signed-off-by: John Mulligan <[email protected]>

Author: phlogistonjohn

MANIFEST.in

@@ -1,3 +1,7 @@
 # Include example files
 recursive-include examples *
 recursive-include sambacc/schema *.json *.yaml
+# embedded data files for grpc
+recursive-include sambacc/grpc/protobufs *.proto
+# embedded data files for varlink
+recursive-include sambacc/varlink/interfaces *.varlink