Add basic heap profiler

[rdettai]

Description

This PR adds a very lightweight, feature gated, heap profiling endpoint.

Using the jemalloc native profiling is complicated, it's hard to asses its performance impact, and the resulting traces are hard to interpret.

This PR proposes an custom and simple heap profiler:

• written so that the profiler has almost no performance impact when it's not being used actively. Every allocation/deallocation simply checks for an atomic ENABLED flag with relaxed ordering and does no extra work if that flag is false.
• the profiler can be activated with a webservice. It logs all allocations larger than a given (configurable) threshold. Instead of printing the entire backtrace, we focus on the first "quickwit related" symbol name (quickwit, chitchat, tantivy)

When started, the profiling allocates ~30MB of symbols.

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