Added execution plan in order to improve async file processing

[norberttech]

Change Log

Added

• Pipeline Execution Plan

Fixed

Changed

Removed

Deprecated

Security

---

Description

So the goal of the pipeline execution plan is to make it possible to process the logical plan and optimize/change it by the processor before actual execution.

Currently implementation mostly aims to simplify two things:

1. Single place where SaveMode is interpreted
2. Async processing of file to file fixes

This PR also unifies the behavior of SaveMode:

• Append - only available in "thread_safe" flow context where the path is always treated as a folder and new files are just appended into it
• Overwrite - path is always removed before processing the pipelines
• IgnoreIfExists - loaders that are going to try to load into the existing location are skipped
• ExceptionIfExists - if any loader is going to try to load into the existing location exception is thrown

Potential futuristic benefits of having an Execution Plan and Execution Processors:

• Optimization of the pipelines (transformers mostly) even before execution
• Calculation pipeline execution complexity
• Early errors detection
• Visualization of the execution plan

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR.

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR.

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR.

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR.