Make workspace configurable for jdtls.

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Closes #34

This PR affects only Eclipse JDTLS and introduces no breaking changes.
It adds the ability to specify the workspace directory path used by the JDTLS server through the MultilspyConfig class:

class MultilspyConfig:
    ...
    ws_path: Path = None
    temp_workspace: bool = False
    ...

By default, the ws_path property is None, and Eclipse JDTLS creates a new workspace for the current project. If the temp_workspace config property is set to false, Eclipse JDTLS will register the new workspace and associate it with the current project. This association is persisted in a file named ws_table in the Eclipse JDTLS directory.

Upon stopping, the server will clean up the new workspace if temp_workspace is true. If the workspace path was provided by the client, the behavior remains similar, except that the workspace is not removed even if temp_workspace is set to true.

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