Update rlp requirement from ~=0.6.0 to ~=4.0.0 in /server

Updates the requirements on [rlp](https://github.com/ethereum/pyrlp) to permit the latest version.
- [Changelog](https://github.com/ethereum/pyrlp/blob/main/docs/release_notes.rst)
- [Commits](ethereum/pyrlp@v0.6.0...v4.0.0)

---
updated-dependencies:
- dependency-name: rlp
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

server/requirements.txt

@@ -6,6 +6,6 @@ aiosqlite~=0.10.0
 base58~=1.0.0
 indy_vdr~=0.3.4
 cchardet~=2.1.0
-rlp~=0.6.0
+rlp~=4.0.0
 supervisor~=4.0.4
 pynacl~=1.5.0