Override sharded-slab to increase MAX_THREADS (#4122)

Add patch directive to Cargo.toml to use patched version of
sharded-slab:
https://github.com/neondatabase/sharded-slab/commit/98d16753ab01c61f0a028de44167307a00efea00

Patch changes the MAX_THREADS limit from 4096 to 32768. This is a
temporary workaround for using tracing from many threads in safekeepers
code, until async safekeepers patch is merged to the main.

Note that patch can affect other rust services, not only the safekeeper
binary.

Cargo.lock

@@ -3960,8 +3960,7 @@ dependencies = [
 [[package]]
 name = "sharded-slab"
 version = "0.1.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "900fba806f70c630b0a382d0d825e17a0f19fcd059a2ade1ff237bcddf446b31"
+source = "git+https://github.com/neondatabase/sharded-slab.git?rev=98d16753ab01c61f0a028de44167307a00efea00#98d16753ab01c61f0a028de44167307a00efea00"
 dependencies = [
  "lazy_static",
 ]

Cargo.toml

@@ -161,11 +161,17 @@ rstest = "0.17"
 tempfile = "3.4"
 tonic-build = "0.9"
 
+[patch.crates-io]
+
 # This is only needed for proxy's tests.
 # TODO: we should probably fork `tokio-postgres-rustls` instead.
-[patch.crates-io]
 tokio-postgres = { git = "https://github.com/neondatabase/rust-postgres.git", rev="0bc41d8503c092b040142214aac3cf7d11d0c19f" }
 
+# Changes the MAX_THREADS limit from 4096 to 32768.
+# This is a temporary workaround for using tracing from many threads in safekeepers code,
+# until async safekeepers patch is merged to the main.
+sharded-slab = { git = "https://github.com/neondatabase/sharded-slab.git", rev="98d16753ab01c61f0a028de44167307a00efea00" }
+
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