[FR] Documentation improvement: Technical Architecture

### Willingness to contribute

Yes. I can contribute a fix for this bug independently.

### Feature Request Proposal

We only have a very concise section in here: https://github.com/linkedin/feathr/blob/main/docs/dev_guide/new_contributor_guide.md#technical-architecture.

We need to expand this into greater details.

### Motivation

> #### What is the use case for this feature?
We only have a very concise section in here: https://github.com/linkedin/feathr/blob/main/docs/dev_guide/new_contributor_guide.md#technical-architecture. We should expand it into greater details so new developers can easily ramp up.

### Details

Write a page-long(or even several pages) wiki for this.

### What component(s) does this bug affect?

- [X] `Python Feathr Client`: This is the client users use to interact with most of our API. Mostly written in Python.
- [X] `Computation Engine`: The computation engine that execute the actual feature join and generation work. Mostly in Scala and Spark.
- [X] `Feature Registry API Layer`: The storage layer supports SQL, Purview(Atlas). The API layer is in Python(FAST API)
- [X] `Feature Registry Web UI layer`: The Web UI for feature registry. Written in React with a few UI frameworks.