doctl registry login error: docker-credential-secretservice: executable file not found in $PATH

**Describe the Issue:**

`doctl registry login` generates an error:
```
Error: error storing credentials - err: exec: "docker-credential-secretservice": executable file not found in $PATH, out: ``
```

I'm following steps as described [here](https://www.digitalocean.com/docs/images/container-registry/quickstart/#push-to-your-registry). Doctl is setup correctly, I am connected to the correct team, the right context is selected and the registry has been created.

Also, `doctl registry config` returns a legitimate result. all the setup seems fine.

**Environment:**

- doctl version 1.47.0-release
- Git commit hash: 77fe6a5d
- OS: Ubuntu 18.04.5 LTS
- Installation method: snap

**Additional Details:**
The first time I ran the command, I got an error about permissions:
```
~$ doctl registry login
Logging Docker in to registry.digitalocean.com
WARNING: Error loading config file: /home/coo/.docker/config.json: open /home/coo/.docker/config.json: permission denied
Warning: Using the doctl Snap? Grant access to the doctl:dot-docker plug to use this command with: sudo snap connect doctl:dot-docker
Error: open /home/coo/.docker/config.json761575089: permission denied
```

I executed said command `sudo snap connect doctl:dot-docker` and afterwards I got the error above.

Note that the secret service binary does exist and is available in `/usr/bin`
```
~$ which docker-credential-secretservice
/usr/bin/docker-credential-secretservice
```

I'm almost certain that this is something to do with the isolation of snap applications. If I had to guess, I'd say the environment the snap runs in doesn't have the path variables, or the access to `/usr/bin`. But that's a, perhaps unhelpful, guess.