chore: remove udb as a dependency of envoy-client (#4587)

# Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
- [ ] This change requires a documentation update

## How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my feature works
- [ ] New and existing unit tests pass locally with my changes

Author: NathanFlurry

engine/packages/util-serde/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "rivet-util-serde"
+version.workspace = true
+authors.workspace = true
+license.workspace = true
+edition.workspace = true
+
+[dependencies]
+indexmap.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+thiserror.workspace = true