[IMP] sales: added customer signature tab shown in developer mode

[fw-bot]

• Removed center align code on images.
• Applied bold style where needed.
• Added new sub section, View online signatures in Developer Mode, to Order confirmations with online signatures section. Section details how to view the Customer Signature tab in a sales order when in Developer Mode.

This 17.0 PR can be FWP up to master.

Task link: https://www.odoo.com/odoo/my-tasks/5239750
Original task link

Forward-Port-Of: #15138

[robodoo]

[fw-bot]

@meval1006 cherrypicking of pull request #15138 failed.

stdout:

CONFLICT (file location): content/applications/sales/sales/send_quotations/get_signature_to_validate/customer-signature-tab.png added in c78938f015415400bf455e7325d81d05694e4887 inside a directory that was renamed in af5b0c610c42c2ed30e8792def6bfaf295640fa6, suggesting it should perhaps be moved to content/applications/sales/sales/sales_quotations/get_signature_to_validate/customer-signature-tab.png.

Either perform the forward-port manually (and push to this branch, proceeding as usual) or close this PR (maybe?).

In the former case, you may want to edit this PR message as well.

⚠️ after resolving this conflict, you will need to merge it via @robodoo.

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

[meval1006]

@robodoo r+

[robodoo]

This PR is already reviewed, reviewing it again is useless.