Command: Fablo connect to join existing cluster / instance of the network

Probably a good PoC of the feature is to support the following scenario:
1. In the directory `./network1` start a fablo network (`fablo init && fablo up`)
2. In the another directory: `./network2`:
a. Prepare `fablo-config.json` with single peer from Org1 (the same org as in `network1`), and a reference to CA (?), certs (?), whatever is required to access another network. We need to determine the structure of the new file and what information is required.
b. Run `fablo up`.
c. The second network starts a peer which joins the `./network1`, channels.

Ultimately we should be able to join a peer, orderer, maybe even run chaincodes. But for a start supporting just the peer is sufficient.

The `./network/fablo-config.json` file may look as follows:

```json
{
"$schema": "https://github.com/hyperledger-labs/fablo/releases/download/2.4.3/schema.json",
"global": {
"fabricVersion": "3.1.0",
"tls": true
},
"orgs": [
{
"organization": {
"name": "Org1",
"domain": "org1.example.com",
"mspName": "Org1MSP"
},
"ca": {
"url": "...",
"tlsCACertPath": "..."
},
"peer": {
"instances": 1
}
}
],
"channels": [
{
"name": "my-channel1",
"orgs": [
{
"name": "Org1",
"peers": [
"peer0"
]
}
]
}
]
}
```

PR addressing the issue should have an additional test script executed in github actions, similar to other test scripts in `e2e-network/docker`.