docs: correct profiling feature name and jemalloc env var (#20030)

Author: Galoretka

docs/vocs/docs/pages/run/faq/profiling.mdx

@@ -33,7 +33,7 @@ Reth includes a `jemalloc` feature to explicitly use jemalloc instead of the sys
 cargo build --features jemalloc
 ```
 
-While the `jemalloc` feature does enable jemalloc, reth has an additional feature, `profiling`, that must be used to enable heap profiling. This feature implicitly enables the `jemalloc`
+While the `jemalloc` feature does enable jemalloc, reth has an additional feature, `jemalloc-prof`, that must be used to enable heap profiling. This feature implicitly enables the `jemalloc`
 feature as well:
 
 ```