Update caikit requirement from <0.17.0,>=0.15.0 to >=0.15.0,<0.19.0

Updates the requirements on [caikit](https://github.com/caikit/caikit) to permit the latest version.
- [Release notes](https://github.com/caikit/caikit/releases)
- [Changelog](https://github.com/caikit/caikit/blob/main/releases.md)
- [Commits](caikit/caikit@v0.15.0...v0.18.0)

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

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

pyproject.toml

@@ -14,7 +14,7 @@ classifiers=[
     "License :: OSI Approved :: Apache Software License"
 ]
 dependencies = [
-    "caikit>=0.15.0,<0.17.0",
+    "caikit>=0.15.0,<0.19.0",
     "ray[default]==2.6.3",
     "pydantic<2"
 ]