Mantine UI: Test scalability

[saswatamcode]

Since new UI has some PromLens query builder features that might end up fetching all series or all label values of a series, would be good to test out if this is scalable and doesn't cause OOMs etc with too many requests.

We might need to implement some pagination otherwise.

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