Support private IPFS networks (via swarm.key)

**Is your feature request related to a problem? Please describe.**
Yes! Private IPFS networks, which are supported in kubo, are not currently enabled in IPFS Desktop.
#950 mentions this, but was closed because swarm.key is not supported.

Additionally, the "this feature is not supported" error message showed in that first issue seems to be broken:

**Describe the solution you'd like**
I would like IPFS Desktop to allow users to connect to a private IPFS network using the configured swarm.key file stored at $IPFS_PATH/swarm.key (following the instructions here: https://github.com/ahester57/ipfs-private-swarm#2-generate-swarmkey)

**Describe alternatives you've considered**
The alternative is to use kubo CLI to run a private network, which is not viable becuase it is not user friendly for non technical users of IPFS.

**Additional context**
I work on the Social Impact team at the Filecoin Foundation, and some of our projects are looking to run private archival networks using IPFS. While the swarm key approach will allow technical users to manage a private network that replicates data, for smaller community archives and art galleries without strong in house technical support, being able to access the data on this private network via a friendly user interface is a critical requirement.