Revamp design page

[ektravel]

Description

This PR revamps the Design section of the documentation as follows:

• Adds a new subsection called Services to the sidebar
• Adds an updated Druid architecture diagram
• Moves "Storage design" section out of design.md and into its own topic
• Moves "Query processing" section out of design.md and into its own topic
• Consolidates the information in "Design" and "Processes and servers" topics
• Removes "Processes and servers" topic from the sidebar
• Replaces "process" with "service"
• Adds a redirect for processes.md

Preview

https://druid-98c2egkpg-katyamacedo-bigcommerce.vercel.app/docs/latest/design/architecture

This PR has:

• been self-reviewed.

[techdocsmith]

I think this is mostly OK. However, I think it would be worth it to get clarity on the router, which seems really out of date.

[techdocsmith]

LGTM after spelling fixes:

    ../docs/design/architecture.md
      115 | Colocating Druid services by server type 

    ../docs/design/coordinator.md
       79 | of segments across Historical servicees in the cluster, the Coordinat 

    ../docs/design/router.md
       26 | roker routes queries based on preconfigured [data retention rules](../ope 

[a2l007]

Looks like the word Historicals is misspelt on the architecture diagram.
@ektravel If you have the source image handy, It would be great if you could fix this.

[ektravel]

@a2l007 Thank you for bringing it to my attention. I will update the source image.