Add ⚡️ content to `Payments` > `Transactions`

[GBKS]

First step is to review the page for additions and changes.

Ideas:

• Add ideas for changes here...

[Bosch-0]

Quick overview recommendations:

• Change title from Transactions overview to What is a bitcoin payment?
• Change the focus giving a big picture overview of how the Lightning network works:
  • Channel construction - could salvage some of the current content around what a transaction is for this.
  • Lifecycle of a payment channel.
  • Overview of routing on LN
  • Payments structure (HTLCs onion wrapping etc.)
  • Lightning network fees.

We should keep a lot of this on-chain content for in the future when we eventually focus on an on-chain vault type product case study.

Happy to tackle this page if no one else is offering.