Add options to add custom values to use in various places in the config

[daniel1302]

Currently, We need to spend a lot of time to change one value, e.g log level. We can add a mechanism, that injects custom context into the config template.

This is a PR that shows problem: https://github.com/vegaprotocol/system-tests/pull/636

Solution

Let's say we have a new section in the HCL config:

template_variables = {
    log_level_vega = "Info"
    log_level_data_node = "Debug"
}

Then We can use it in a configs like here:

// ============================
// ===== VegaNode Config ======
// ============================

      vega = <<-EOT
[API]
  	Level = "{{.variables.log_level_vega}}"
	Port = 30{{.NodeNumber}}2
	[API.REST]
			Port = 30{{.NodeNumber}}3

[Blockchain]
  	Level = "Debug"
	[Blockchain.Tendermint]
    	Level = "{{.variables.log_level_vega}}"
		ClientAddr = "tcp://127.0.0.1:266{{.NodeNumber}}7"
		ServerAddr = "0.0.0.0"
		ServerPort = 266{{.NodeNumber}}8
	[Blockchain.Null]
    	evel = "{{.variables.log_level_vega}}"
		Port = 31{{.NodeNumber}}1

[Collateral]
    Level = "{{.variables.log_level_vega}}"

[CoreAPI]
    LogLevel = "{{.variables.log_level_vega}}"
...
...