Add lemminx lsp

[someone13574]

It would be nice if this extension could support the lemminx language server. Note that you will need CI in the repo to build it since they don’t release binaries.

If nobody else wants to work on it, I can probably find time at some point soon.

[fbricon]

FYI, Red Hat builds and releases the binaries in https://github.com/redhat-developer/vscode-xml/releases/tag/0.27.1