feat: common party accounting

[nextchamp-saqib]

The PR incorporates the solution of this app for handling scenarios where sales invoices/purchase invoices are to be made against suppliers/customers

The solution proposed by the app is to:

• Create a journal entry on the submission of Sales Invoices against a customer which has the primary role of a supplier.
• The journal entry will reconcile the newly created sales invoice and converts the invoice balance into an advance against the supplier
• This advance can be used to reconcile purchase invoices against the supplier

A new doctype Party Link is introduced to link a customer with a supplier.

A new toggle is added to accounts settings to enable/disable the automatic creation of the journal entry.

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Thanks @ahmadpak for the solution!

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Docs: https://docs.erpnext.com/docs/v13/user/manual/en/accounts/articles/common_party_accounting

[ahmadpak]

My pleasure @nextchamp-saqib