[ADD] purchase: import vendor pricelist

[Felicious]

New doc on formatting and importing vendor pricelists in bulk.

• Defines important fields for importing vendor pricelists, like Vendor, Product Template, Sequence
• Detailed instructions on External ID lookup
• Include examples of sample CSV and XLSX files for reference.
• Detailed instruction of exporting vendor pricelists

Received help from import/export expert, @chrp-odoo

Task

FWport: yes :D

[robodoo]

[Felicious]

Hello @kekiss ! This import PR is ready for your first round of peer review. This is your scope, so feel free to leave many comments~ :blush:

I'm open to any and all feedback, particularly structure. If you think there's a better way to reorganize any of this info, feel free to share :blush: Let's collaborate :heart:

[Felicious]

Received review from @chrp-odoo. While implementing his suggestions, this PR will be converted to draft mode (:

[Felicious]

Hello @odoo/us-doc-review ! This PR is ready for final review!

[Felicious]

Hello @samueljlieber ! This PR is ready for technical review :smile:

[Felicious]

@robodoo r+