Docs: Add "Working with Data" section

[hacksparrow]

We have enough feature to create the section and content as in the LB3 docs - https://loopback.io/doc/en/lb3/Working-with-data.html.

Acceptance Criteria

Add the Working with data in LB4 docs, as a similar content and structure as https://loopback.io/doc/en/lb3/Working-with-data.html. Make sure the content is correct and relevant to LoopBack 4

• Working with data
  • Creating, updating and deleting data
  • Querying data (higher priority)
• Look at Repositories for LB4 and add what's missing from the Working with Data pages from LB3
  • this content will go underneath this section of the page.

Out of scope

The following section is out of scope for this task:

• Advanced topics: data

[dhmlau]

@hacksparrow , could you please review the acceptance criteria below? I intentionally didn't put the advanced topic here, perhaps we can do it incrementally. There's one about socket.io but not sure if it falls under the advanced topic. https://github.com/raymondfeng/loopback4-example-websocket

Acceptance Criteria

Add the Working with data in LB4 docs, as a similar content and structure as https://loopback.io/doc/en/lb3/Working-with-data.html.

• Working with data
  • Creating, updating and deleting data
  • Querying data
• For each topic, verify the content is correct (including links and methods) and relevant to LoopBack 4
• No advanced topics for this version
• Look at Repositories for LB4 and add what's missing from the Working with Data pages from LB3
  • this content will go underneath this section of the page.

Note some of the content will need to be modified to fit LoopBack 4, such as @emonddr's comment:

This LB3 section https://loopback.io/doc/en/lb3/Working-with-data.html needs to be rewritten for LB4 to discuss the CRUD methods of a repository (instead of a model), and its relationship with controller endpoints.

[bajtos]

I intentionally didn't put the advanced topic here, perhaps we can do it incrementally.

+1 to leave advanced topics out of the initial version.

[emonddr]

This LB3 section https://loopback.io/doc/en/lb3/Working-with-data.html needs to be rewritten for LB4 to discuss the CRUD methods of a repository (instead of a model), and its relationship with controller endpoints.