[FW][IMP] payment_stripe: support webhooks

[fw-bot]

Allow configuring a webhook in Stripe to send s2s notifications to Odoo
when a Checkout payment is completed. Note that SetupIntent and
PaymentIntent events are not listened to, since they are handled 'live'
with the customer actively present; the main use case for Stripe
webhooks is a Checkout session that gets interrupted before the customer
is redirected to Odoo (e.g. network loss, browser crash, closing the
tab, etc.).

The webhook should be configured to send its events to
<base_url>/payment/stripe/webhook and should only subscribe to
checkout.session.completed events to avoid spamming the Odoo server with
useless notifications.

opw-2488452
opw-2451463
opw-2449738

BACKPORT of commit: dc4f6ad

Should not be merged beyond 14.0 (14.0 excluded)

Forward-Port-Of: #71520
Forward-Port-Of: #69809

[robodoo]

[fw-bot]

Ping @simongoffin
Cherrypicking f806dad of source #69809 failed

stderr:

15:46:08.358470 git.c:344               trace: built-in: git cherry-pick f806dad74daf1a95ce0b02b6088859824d9d626b
error: could not apply f806dad74da... [IMP] payment_stripe: support webhooks
hint: after resolving the conflicts, mark the corrected paths
hint: with 'git add <paths>' or 'git rm <paths>'
hint: and commit the result with 'git commit'
----------
status:

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.

[xmo-odoo]

@robodoo override=ci/security

cf source pr

[Xavier-Do]

@simongoffin there is an upgrade exception active for this pr.
Please forwardport this asap.

[wtaferner]

❗ Do not forward port without merging #71933 before

[AdrienHorgnies]

@simongoffin
I've added my changes to fix this FW commit into a separate commit, so you can inspect them separately. We can squash it into the 1st commit when review is done.

I fixed all unit tests, and tested the full flow using stripe test environment with success.
However, I had to make changes that makes me wonder if this module actually works in other versions.
Especially, the code assumes the object charge contains a metadata dictionary that contains a reference key.
I didn't find it during my tests. And as my mocks were copy and paste from stripe API responses, I conclude that Stripe is doing something differently (mocks were written in odoo version 14.0 a few months ago). I checked documentation, and this metadata field should exist... Anyway, I fixed this using a safe statement that won't break anything:

if 'metadata' in data and not data.get('metadata').get('reference'):
                data['metadata']['reference'] = reference

[simongoffin]

robodoo r+