[GUIDE] An edge node setup for multiple Mithril signers

## Why

Addressing security concerns with the Mithril software setup outlined in issue [1586](https://github.com/input-output-hk/mithril/discussions/1586).

## What

**A quick setup guide for Mithril supporting multiple pools on a single isolated relay server.**

OS: Ubuntu 22.04

(0) Configure and sync a Cardano mainnet relay in the folder `/home/ubuntu/relay/` with database path `/home/ubuntu/relay/db` and socket path `/home/ubuntu/relay/db/socket`. Setup `cardano-cli v8.9.0` in `/home/ubuntu/.local/bin/cardano-cli`. Copy `kes.skey` and `node.cert` to the folder `/home/ubuntu/relay/1/`.

(1) Install Mithril in `/opt/mithril/`

```
sudo mkdir -p /opt/mithril
sudo chown ubuntu /opt/mithril
sudo chgrp ubuntu /opt/mithril

cd /opt/mithril
wget https://github.com/input-output-hk/mithril/releases/download/2408.0/mithril-2408.0-linux-x64.tar.gz
tar -xzf mithril-2408.0-linux-x64.tar.gz
chmod 755 mithril-signer
chmod 755 mithril-relay
chmod 755 mithril-client
chmod 755 mithril-aggregator

sudo apt install libssl-dev
```

(2) Create environment file `mithril-signer-1.env` for systemd in `/opt/mithril/`.
```
KES_SECRET_KEY_PATH=/home/ubuntu/relay/1/kes.skey
OPERATIONAL_CERTIFICATE_PATH=/home/ubuntu/relay/1/node.cert
NETWORK=mainnet
AGGREGATOR_ENDPOINT=https://aggregator.release-mainnet.api.mithril.network/aggregator
RUN_INTERVAL=60000
DB_DIRECTORY=/home/ubuntu/relay/db
CARDANO_NODE_SOCKET_PATH=/home/ubuntu/relay/db/socket
CARDANO_CLI_PATH=/home/ubuntu/.local/bin/cardano-cli
DATA_STORES_DIRECTORY=/opt/mithril/stores-1
STORE_RETENTION_LIMIT=5
ERA_READER_ADAPTER_TYPE=cardano-chain
ERA_READER_ADAPTER_PARAMS={"address": "addr1qy72kwgm6kypyc5maw0h8mfagwag8wjnx6emgfnsnhqaml6gx7gg4tzplw9l32nsgclqax7stc4u6c5dn0ctljwscm2sqv0teg", "verification_key": "5b31312c3133342c3231352c37362c3134312c3232302c3131312c3135342c36332c3233302c3131342c31322c38372c37342c39342c3137322c3133322c32372c39362c3138362c3132362c3137382c31392c3131342c33302c3234332c36342c3134312c3131302c38332c38362c31395d"}
```

(3) Setup systemd for `mithril-signer-1.service`.
```
sudo bash -c 'cat > /etc/systemd/system/mithril-signer-1.service << EOF
[Unit]
Description=Mithril signer service 1
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=60
User=ubuntu
EnvironmentFile=/opt/mithril/mithril-signer-1.env
ExecStart=/opt/mithril/mithril-signer -vvv

[Install]
WantedBy=multi-user.target
EOF'
```
```
sudo systemctl start mithril-signer-1
sudo systemctl enable mithril-signer-1
systemctl status mithril-signer-1.service
```

(4) Verify Mithril registration and signature
```
wget https://mithril.network/doc/scripts/verify_signer_registration.sh
chmod +x verify_signer_registration.sh
wget https://mithril.network/doc/scripts/verify_signer_signature.sh
chmod +x verify_signer_signature.sh
```
Replace `pool17xextu09ghdfcmsq83whq0a45geg83jxe4qt94sevu087tzdzkl` with your pool id!
```
PARTY_ID=pool17xextu09ghdfcmsq83whq0a45geg83jxe4qt94sevu087tzdzkl AGGREGATOR_ENDPOINT=https://aggregator.release-mainnet.api.mithril.network/aggregator ./verify_signer_registration.sh
PARTY_ID=pool17xextu09ghdfcmsq83whq0a45geg83jxe4qt94sevu087tzdzkl AGGREGATOR_ENDPOINT=https://aggregator.release-mainnet.api.mithril.network/aggregator ./verify_signer_signature.sh
```

(5) Repeat steps (2) and (3) for every additional pool.

(a) Copy `kes.skey` and `node.cert` to the folder `/home/ubuntu/relay/2/`.
(b) Create environment file `mithril-signer-2.env` for systemd in `/opt/mithril/`.
```
KES_SECRET_KEY_PATH=/home/ubuntu/relay/2/kes.skey
OPERATIONAL_CERTIFICATE_PATH=/home/ubuntu/relay/2/node.cert
...
DATA_STORES_DIRECTORY=/opt/mithril/stores-2
...
```
(c) Setup systemd for `mithril-signer-2.service`.
```
sudo bash -c 'cat > /etc/systemd/system/mithril-signer-2.service << EOF
...
Description=Mithril signer service 2
...
EnvironmentFile=/opt/mithril/mithril-signer-2.env
...
```
```
sudo systemctl start mithril-signer-2
sudo systemctl enable mithril-signer-2
systemctl status mithril-signer-2.service
```
(d) Verify Mithril registration and signature for every additional pool id.