feat(docs): add primer on all transaction types

[tcoratger]

Should solve #3803.

I added the description of the different types of transactions in two places:

• In the code for new contributors who would be lost.
• In the official documentation (book) for users with a little more text.

If it is not necessary, I can remove the description in the book, but I thought it could provide additional information.

[codecov]

Codecov Report

Merging #3897 (ceec98b) into main (9b9ae82) will increase coverage by 0.02%.
The diff coverage is n/a.

Files Changed	Coverage Δ
crates/primitives/src/transaction/mod.rs	82.22% <ø> (ø)

... and 9 files with indirect coverage changes

Flag	Coverage Δ
integration-tests	15.54% <ø> (-0.02%)	⬇️
unit-tests	64.44% <ø> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
reth binary	26.44% <ø> (ø)
blockchain tree	83.01% <ø> (ø)
pipeline	89.66% <ø> (ø)
storage (db)	74.19% <ø> (ø)
trie	94.70% <ø> (+0.05%)	⬆️
txpool	46.56% <ø> (+0.56%)	⬆️
networking	77.67% <ø> (-0.02%)	⬇️
rpc	58.28% <ø> (ø)
consensus	64.46% <ø> (+0.13%)	⬆️
revm	33.68% <ø> (ø)
payload builder	6.61% <ø> (ø)
primitives	88.01% <ø> (ø)

[mattsse]

awesome!

I will use this as the base and extend this with docs about reth's internal transaction types (txpool, primitives) and rpc types