git: Fix missing reverse indices for some Git commands
While most of our commands that may end up writing packfiles are set up correctly to write reverse indices, both git-receive-pack(1) and git-fetch(1) are missing the configuration. As a result, packfiles written by them are missing the indices. More generally though, they're missing all packfile-related configuration like the number of threads they're supposed to use.
Fix this by adding the packfile configuration to both commands.
Fixes #4352 (closed).