Write TypeScript guide

[shaydewael]

Description

While the Using TypeScript page exists, it's very unhelpful and doesn't explain how Bolt's type system works, or how to refine/customize types.

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• example code related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

[filmaj]

Setting this to the 5.0.0 milestone which is when we plan to revamp the type system in bolt.