Upgrade ClickHouse

We're currently running ClickHouse 23.8.7.1, from just over two years ago. ClickHouse has improved since then, and I'd like to consider upgrading, both for features and performance. Some motivations:

• We're missing potentially useful features. As mentioned in #9256, we might be able to use newer features like Variant types and the merge() table function to improve performance, but those features either aren't supported or don't work well in ClickHouse v23.
• When we encounter an expected behavior in ClickHouse, we have to ask whether it's been fixed in a newer version. For example, issues like #9234 and #8595 might be resolved in newer ClickHouse versions. Having to look up code and docs for older versions will slow down investigations.
• Newer ClickHouse versions perform better. I don't have an oximeter-specific benchmark at the moment (although I wonder if we should put one together), but I ran clickbench against a few different ClickHouse versions, and that benchmark dropped execution time by about 33% from v23 to v25. Will add more details on that below.

Somewhat arbitrarily, I want to propose upgrading to an lts release in the v24 series. Jumping two major releases sounds risky, and maybe we can upgrade to v25 in 2026. I would also like to document and improve the process of building ClickHouse, and then start doing it on a regular cadence—although maybe that belongs in another ticket or RFD.

cc @bnaecker @andrewjstone @citrus-it

Start by locating the ClickHouse version declaration and build or deployment entry points, then review the compatibility implications of moving from 23.8.7.1 to a v24 LTS release. Check the behavior discussed in #9256, #9234, and #8595, and compare relevant ClickBench results. Done means the target version is agreed, the upgrade works, and the build process is documented if it remains in scope.