Add a method to set frontendHotdeployDependencies via Gradle plugin in gradle.build file

### Describe your motivation

It is possible to define frontendHotdeployDependencies via system property, see: https://github.com/vaadin/docs/pull/4174

It would be more friendly DX if this setting could defined in gradle.build file

### Describe the solution you'd like

Add the property to gradle plugin so that it can be set in gradle.build file
