[VSCode extension] Add a folder-level setting to specify a custom JDK for running Maven

### Description

Currently, all Maven invocations use the `netbeans.jdkhome` JDK. However, I'd like a folder-level setting to be able to specify a custom JDK for running Maven.

Previous issue: https://issues.apache.org/jira/browse/NETBEANS-5408

### Use case/motivation

* be able to run the language server with the latest JDK, while using specific JDKs to build specific projects

### Related issues

#4482

### Are you willing to submit a pull request?

No

### Code of Conduct

Yes

Start by tracing the VSCode extension's Maven invocations and the existing netbeans.jdkhome setting; no source files or tests are identified in the issue. Done means a folder-level JDK setting controls Maven builds while the language server can continue using the configured latest JDK.

Written by the indexing model from the issue text.