Inconsistent behaviour between command line arguments and config file

[fruzitent]

Issue

containerd-cni-binary-dir and containerd-cni-config-path do work,
but worker.oci.cniBinaryPath and worker.oci.cniConfigPath do not.

Steps to reproduce

1. Get nerdctl to generate default configuration it wants
   [1],

   and replace "cniVersion": "1.0.0" with 0.3.0 because of ?
   [1]
   [2].

   // C:\Program Files\containerd\cni\conf\nerdctl-nat.conflist
   {
       "cniVersion": "0.3.0",
       "name": "nat",
       "nerdctlID": "d919a100ce6b45524d415d52d088d5817587c6dd8c3691b03b8063c44d043523",
       "nerdctlLabels": {
       "nerdctl/default-network": "true"
       },
       "plugins": [
       {
           "ipam": {
           "routes": [
               {
               "gateway": "10.4.0.1"
               }
           ],
           "subnet": "10.4.0.0/24",
           "type": ""
           },
           "master": "Ethernet",
           "type": "nat"
       }
       ]
   }

2. Point buildkitd to use this via command line arguments.

   $ buildkitd `
       --containerd-cni-binary-dir "${Env:ProgramFiles}\containerd\cni\bin\" `
       --containerd-cni-config-path "${Env:ProgramFiles}\containerd\cni\conf\nerdctl-nat.conflist" `
       ;
   {"level":"debug","msg":"creating new network namespace cwc38k39ai9prgrbkc6xj53td","time":"2024-03-19T05:53:12+02:00"}

   It works!

3. Put the same settings in config file
   [1].

   # C:\ProgramData\buildkitd\buildkitd.toml
   [worker.oci]
   cniBinaryPath = "C:\\Program Files\\containerd\\cni\\bin"
   cniConfigPath = "C:\\Program Files\\containerd\\cni\\conf\\nerdctl-nat.conflist"

   It was able to use debug and log.format options successfully,
   but suddenly cni stops working.

   Neither of the cmd or pwsh variables, full path with forward or backward slashes - none of this matters,
   these fields are simply ignored for some reason.

4. Copy nat.exe to C:\ProgramData\buildkitd\bin
   [1],
   as well as regular cni conf
   [2]
   [3],
   instead of conflist (it used to work when run from the command line).

   // C:\ProgramData\buildkitd\cni.json
   {
       "cniVersion": "0.3.0",
       "name": "nat",
       "type": "nat",
       "master": "Ethernet",
       "ipam": {
       "subnet": "10.4.0.0/24",
       "routes": [
           {
           "gateway": "10.4.0.1"
           }
       ]
       },
       "capabilities": {
       "portMappings": true,
       "dns": true
       }
   }

   $ buildkitd
   {"level":"debug","msg":"creating new network namespace 9yptgzxgas0nvj7ct3dev27lh","time":"2024-03-19T06:09:57+02:00"}

   It works!

Version

$ buildkitd --version
buildkitd github.com/moby/buildkit v0.13.1 2ae42e0c0c793d7d66b7a23424af6fd6c2f9c8f3
$ containerd --version
containerd github.com/containerd/containerd v1.7.14 dcf2847247e18caba8dce86522029642f60fe96b
$ nerdctl --version
nerdctl version 1.7.5

[tonistiigi]

equivalent to containerd-cni-binary-dir would be

[worker.containerd]
cniBinaryPath =