Docs: Updated and refined node installation guide

[itrocket-team]

Updates for the Node Installation guide:

• Added variables for .bash_profile in the beginning of installation for more convenience;
• Added go installation commands;
• All necessary changes in client.toml, config.toml, and app.toml are now made with commands, not manually;
• Optional custom ports configuration is added;
• Node start now has 2 options: from CLI or with a service file;
• Added one-command autoinstallation developed by us. It installs all the necessary dependencies, installs the binary and configures the node (edits configuration files, downloads genesis and addrbook, sets seeds and peers), downloads a snapshot, and runs the node with a service file.

Also, we've added ITRocket pruned snapshot to the list.