MantineUI: Port over parse_expr endpoint and make it work with explain/analyze

[saswatamcode]

As part of new UI we get some PromLens features, one of which is a query tree parser and explainer.

We should try to port this over, and also hook in the Thanos Query Engine explain/analyze features with it.

We would need some modifications for extra analyze button.

We would need to add content for the Thanos engine operators as well, and manage PromQL query tree and Thanos engine query tree in sane way (maybe one more option to see engine query tree, after you display PromQL query tree?)

https://github.com/thanos-io/thanos/tree/mantine-ui-port

[saswatamcode]

cc: @MichaHoffmann assigning you to this as we talked about :)