Add support for proxy and authenticator configuration in the Admin API tool window

Some advanced configuration options like proxying and authenticator are not currently supported, so see how it could be implemented.

Introduce a new button on the Admin API panel toolbar for the configuration.
- This button would open up a dialog window in which the mentioned options could be specified.
These values would be stored in an application-level persistent component service (on users' local machines) except sensitive data.
- As for API tokens and passwords, the first option is to use com.intellij.ide.passwordSafe.PasswordSafe.
- For alternatives, look into other plugins like the GitHub or SonarLint ones, how those handle API token storage in a safe way.

picimako / wiremocha