feat: split xgboost_abalone and model_deploy project templates

[kukushking]

Describe your changes

• Separate xgboost_abalone and model_deploy project templates into two separate templates - for an example SageMaker pipeline training on abalone dataset with XGBoost, and for CI/CD template for deploying model endpoint based on the package/group to a set of 3 accounts (dev, pre-prod, and prod).
• Add template links to the main readme
• Add architecture diagrams for the individual templates

Issue ticket number and link

• [FEATURE] Separate model deployment pipeline from multi-acc Abalone/XGBoost template #41

Checklist before requesting a review

• I updated CHANGELOG.MD with a description of my changes
• If the change was to a module, I ran the code validation script (scripts/validate.sh)
• If the change was to a module, I have added thorough tests
• If the change was to a module, I have added/updated the module's README.md
• If a module was added, I added a reference to the module to the repository's README.md
• I verified that my code deploys successfully using seedfarmer apply

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[LeonLuttenberger]

Great work!