fix: update rocksdb from v0.19 to v0.21

Depending on the C++ toolchain used by the underlying system, builds of
rocksdb might fail because of an issue documented in:

facebook/rocksdb#11118

(In short, the code relied on headers importing other headers, rather
than what the standard guarantees headers to export; thus code may not
compiler on all toolchains).

Version 0.21 of the crate fixes this issue, by relying on a later
version of the underlying rocksdb library.

For the rust crate, this issue showed up in:

rust-rocksdb/rust-rocksdb#772

On Linux/Manjaro I ran into this issue as well, but I expect that other
people following along with the docs might run into it as well, so
probably worth updating, unless there's some issue with doing so.

crates/bin/pd/Cargo.toml

@@ -104,7 +104,7 @@ ed25519-consensus = "2"
 async-trait = "0.1.52"
 tendermint-rpc = { version = "0.32.0", features = ["http-client"] }
 once_cell = "1.7.2"
-rocksdb = "0.19.0"
+rocksdb = "0.21.0"
 tempfile = "3.3.0"
 base64 = "0.20"
 console-subscriber = "0.1.8"

crates/storage/Cargo.toml

@@ -13,7 +13,7 @@ tempfile = "3.3.0"
 anyhow = "1"
 async-trait = "0.1.52"
 tracing = "0.1"
-rocksdb = "0.19.0"
+rocksdb = "0.21.0"
 futures = "0.3"
 hex = "0.4"
 metrics = "0.19.0"