docs: update tx pool to reflect RLP hex storage instead of tx hash

[bootcodes]

Description

This PR updates docs/nonce-management-and-tx-pool.md to reflect the actual store values for the transaction pool.
Replaces tx hash by RLP encoded transaction in the following sections :
### Storage backends
and
#### eth_sendRawTransaction

Related issue(s)

Fixes #5067

Testing Guide

Changes from original design (optional)

N/A

Additional work needed (optional)

N/A

Checklist

• I've assigned an assignee to this PR and related issue(s) (if applicable)
• I've assigned a label to this PR and related issue(s) (if applicable)
• I've assigned a milestone to this PR and related issue(s) (if applicable)
• I've updated documentation (code comments, README, etc. if applicable)
• I've done sufficient testing (unit, integration, etc.)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

❌ Your project check has failed because the head coverage (72.99%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (ceba217) and HEAD (a5509da). Click for more details.

HEAD has 20 uploads less than BASE

Flag	BASE (ceba217)	HEAD (a5509da)
	21	5
config-service	1	0
relay	1	0
server	1	0
ws-server	1	0

@@             Coverage Diff             @@
##             main    #5075       +/-   ##
===========================================
- Coverage   95.89%   72.99%   -22.91%     
===========================================
  Files         145      145               
  Lines       24824    24824               
  Branches     1994      836     -1158     
===========================================
- Hits        23806    18120     -5686     
- Misses        990     6688     +5698     
+ Partials       28       16       -12     

Flag	Coverage Δ
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relay	?
server	?
ws-server	?

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