Add kmod component and update depmod path

[bronson]

These changes allow just show-me-the-future to finish on my Bluefin host.

I'm not sure they're correct because now showing-my-future hangs here with no response...

Adding new partition 2 to partition table.
Writing new partition table.
All done.
==> Booting the installed server in QEMU (background)...
==> Polling KubeStellar Console readiness at http://127.0.0.1:8080 (deadline: 600s)...

[bronson]

Rather than pasting some massive logfiles, here's the a summary of what went wrong... Happy to add logfiles if you think they'd be useful.

GLM:

The actual errors observed across the two runs:

Run 1 (log):

  sh: line 19: depmod: command not found                                       
  ... failed with exitcode 127                                                 

→ flatcar/flatcar-kernel.bst — depmod invoked but not present in the build
sandbox (missing kmod build-dep).

Run 2 (log2):

  depmod: ERROR: could not open directory                                      
/buildstream-install/lib/modules/6.12.102-flatcar: No such file or directory   
  ... failed with exitcode 1                                                   

→ Same element — depmod now ran but searched lib/modules while the module tree
lives at usr/lib/modules.

Both runs ended with the same downstream result:

  FAILURE Command failed — flatcar/flatcar-kernel.bst                          
  error: recipe `bst` failed with exit code 255                                
  error: recipe `build-installer` failed on line 102 with exit code 255        
  error: recipe `show-me-the-future` failed with exit code 255                 

In short: error 1 was a missing binary (exit 127), error 2 was a wrong search
path (exit 1), and the 255s were just the failure propagating up through just.