Configuration templating

[aviramha]

Right now our configuration supports constant values, but some users asked for templating features, so they could have a config file that is mutated by the specific run.
I think maybe we should start with adding ability to use environment variables, so for example have

{
  "target": {
    "path": "{DEPLOYMENT_NAME}",
    "namespace": "{NAMESPACE_NAME}"
  }
}

then user can set DEPLOYMENT_NAME and fetch it from env.

[aviramha]

Have to do before:

• Configuration validation from cli #1840
• Use cli for configuration validation mirrord-vscode#57
• Use cli for configuration validation mirrord-intellij#99

[meowjesty]

All 3 requirements have been merged!