Review and improve transaction docs

[nikolasburk]

• the current transaction docs page is the result of a merge of two separate transaction-related pages during the docs restructure end of 2023
• mixes a lot of topics, Prisma-specific but also generally about transactions
• a lot of it was written at a time when Prisma ORM didn't even support interactive transactions, we should review the entire page and see what we actually need and how that should be documented ("how would we document transaction if we were to do it from scratch today")
• more input: https://prisma-company.slack.com/archives/C0599UK7AP8/p1710443796762879