feat: Payments based dunning

[marination]

An attempt to revive #27528

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Related to #26969

Create dunning for all overdue payments of a customer. We use a table similar to the payment schedule in sales invoice to pull all overdue scheduled payments into the Dunning.

• Rate of Interest is the same for all overdue payments.
• Interest amount is calculated for each overdue payment.
• Dunning Fee is applied only once per dunning.

Changes in accounting

• Dunning amount will no longer be booked to receivables. The reason is that the dunning amount is not paid in many cases / is only intended as a warning. If paid, the dunning amount will be recorded as additional income in Payment Entry. See here and here for further reading (in german).

Preview:

Docs: https://docs.erpnext.com/docs/v13/user/manual/en/accounts/dunning?editWiki=1&wikiPagePatch=318ad1abe6
Discuss: https://discuss.erpnext.com/t/dunning-mahnung-warning-notice/49499/30?u=rmeyer

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ToDo:

• Resolve conflicts
• Manual tests of functionality
• Test of migration patch
• Fix: Manually added Payment Schedule without template or terms keeps dunning unresolved. Partial Fix: fix: Payment Term must be mandatory if Allocate Payment based on .. is checked #35798 (users must take care of this. A note is added to the docs)
• Possibly add some unit tests
• Apply changes suggested by reviewers / community
• Check and update the docs

[barredterra]

Tested, LGTM

[marination]

@deepeshgarg007 This is tested, reviewed and ready to merge. You can give it a last check and let us know if it looks okay.

[marination]

@deepeshgarg007 the patch reverses GL entries for unresolved dunnings. Will it be problematic if there are some old unresolved dunnings ? From before the Accounts Frozen Till Date ? Those should stay untouched right ?

[marination]

@Mergifyio backport version-14-hotfix

[mergify]

backport version-14-hotfix

❌ No backport have been created

Details

• Backport to branch version-14-hotfix failed

Git reported the following error:

error: commit e686bb07396428c8c6072a96cd1a789bf902123b is a merge but no -m option was given.
fatal: cherry-pick failed

[muchai]

This could use a backport to version 14 please.

[bosue]

@muchai: This is a massive change, so backporting would break lots of custom code in v14 IMO. Also, it‘s still experimental, so not fully settled in v15. We all loved the feature and wanted to see it in v15, but IMO there‘s still much to do until it may be considered stable and be backported. So instead, you might want to upgrade to v15?

But that‘s just my two cents. I personally don‘t care if it‘s backported. I just can‘t consider it finished, and while having quite many advantages, there‘s a couple of drawbacks, including lost features that should probably be reinstated before backporting.