feat: combine assets into a single folder

[donatas-dt]

Description

Currently there are 4 assets folders - one for each pipeline.

I combined them into one assets folder used for all pipelines. Updated docs, makefile, CI/CD...

How has this been tested?

E2E tests in CI/CD
Release CI/CD tested in forked repo and new gcp projects.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• 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
• New and existing unit tests pass locally with my changes
• I have updated any relevant documentation to reflect my changes
• I have assigned a reviewer and messaged them

Pipeline run links:

https://console.cloud.google.com/vertex-ai/locations/europe-west2/pipelines/runs/tensorflow-prediction-pipeline-20230522091356?project=dt-turbo-templates-staging
https://console.cloud.google.com/vertex-ai/locations/europe-west2/pipelines/runs/xgboost-prediction-pipeline-20230522090420?project=dt-turbo-templates-staging
https://console.cloud.google.com/vertex-ai/locations/europe-west2/pipelines/runs/tensorflow-train-pipeline-20230522085148?project=dt-turbo-templates-staging
https://console.cloud.google.com/vertex-ai/locations/europe-west2/pipelines/runs/xgboost-train-pipeline-20230522085140?project=dt-turbo-templates-staging

[donatas-dt]

/gcbrun