[FW][IMP] sales: added important admonition to amazon docs

[fw-bot]

PROJECT TASK (request for adjustment): https://www.odoo.com/odoo/project.task/3983555?cids=3

Issue: Odoo limitation, can't sell the same product in FBA and FBM (will set 0 as the quantity)

Added IMPORTANT admonition blocks to the 2 Amazon Connector docs (in the Sales app section) that cover FBA and FBM concepts/topics. The admonition alerts the reader of the issue, and informs users that a correction to the issue should be happening in the near future.

This should be Forward-Ported through the latest version of 17...

Forward-Port-Of: odoo/documentation#9780

[robodoo]

[fw-bot]

@ksc-odoo this PR targets master and is the last of the forward-port chain containing:

• odoo/documentation#10107
• odoo/documentation#10105
• odoo/documentation#10104
• odoo/documentation#10103

To merge the full chain, use

@robodoo r+

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port

[ksc-odoo]

@robodoo r+