Fix: enable model monitoring for XGBoost pipeline

[ghost]

Description

Model monitoring metadata isn't persisted during XGBoost training. Further, caching has been disabled for lookup_model components in all pipelines.

Automated tests passed on Datatonic repo https://github.com/teamdatatonic/vertex-pipelines-end-to-end-samples/pull/11

How has this been tested?

• clean model registry
• end-to-end tests (with and without caching)
• ensure that batch prediction jobs return monitoring results

Checklist

• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have successfully run the E2E tests, and have included the links to the pipeline runs below - [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] I have updated any relevant documentation to reflect my changes
• [x] I have assigned a reviewer and messaged them

[ghost]

@Linchin this one is ready to merge!