This should fix the tests, that are currently failing on CI with:
```
2022-07-05 16:19:13,250 259 INFO odoo odoo.service.server: Starting post tests
2022-07-05 16:19:13,253 259 ERROR odoo odoo.tests.loader: Can not `import mail_autosubscribe`.
Traceback (most recent call last):
File "/opt/odoo/odoo/tests/loader.py", line 33, in _get_tests_modules
mod = importlib.import_module('.tests', modpath)
File "/usr/lib/python3.8/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
File "<frozen importlib._bootstrap>", line 991, in _find_and_load
File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
File "<frozen importlib._bootstrap_external>", line 848, in exec_module
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "/__w/social/social/mail_autosubscribe/tests/__init__.py", line 1, in <module>
from . import test_mail_autosubscribe
File "/__w/social/social/mail_autosubscribe/tests/test_mail_autosubscribe.py", line 5, in <module>
from odoo_test_helper import FakeModelLoader
ModuleNotFoundError: No module named 'odoo_test_helper'
```
- FIX bug when split email message by `to_keep` parameter. When the html code is split, it is broken. As a result of this, when it use `fromstring`,
it try to fix this by closing tags.
Example about fixed functionality:
message:
`
<table>
<tr>
<td>
{to_keep}
</td>
</tr>
</table>
`
Split messsage inside `remove_href_odoo` function:
part[0]
`
<table>
<tr>
<td>
`
--------
part[1]
`
</td>
</tr>
</table>
`
-----------------
Result when join by `to_keep`
`
<table>
<tr>
<td>
{to_keep}
</td>
</tr>
</table>
`
Before this patch, the module was designed after the [deprecated Mailgun webhooks][3]. However Mailgun had the [events API][2] which was quite different. Modern Mailgun has deprecated those webhooks and instead uses new ones that include the same payload as the events API, so you can reuse code.
However, this was incorrectly reusing the code inversely: trying to process the events API through the same code prepared for the deprecated webhooks.
Besides, both `failed` and `rejected` mailgun events were mapped to `error` state, but that was also wrong because [`mail_tracking` doesn't have an `error` state][1].
So the logic of the whole module is changed, adapting it to process the events API payload, both through controllers (prepared for the new webhooks) and manual updates that directly call the events API.
Also, `rejected` is now translated into `reject`, and `failed` is translated into `hard_bounce` or `soft_bounce` depending on the severity, as specified by [mailgun docs][2]. Also, `bounced` and `dropped` mailgun states are removed because they don't exist, and instead `failed` and `rejected` properly get their metadata.
Of course, to know the severity, now the method to obtain that info must change, it' can't be a simple dict anymore.
Added more parameters because for example modern Mailgun uses different keys for signing payload than for accessing the API. As there are so many parameters, configuration is now possible through `res.config.settings`. Go there to autoregister webhooks too.
Since the new webhooks are completely incompatible with the old supposedly-abstract webhooks controllers (that were never really that abstract), support for old webhooks is removed, and it will be removed in the future from `mail_tracking` directly. There is a migration script that attempts to unregister old webhooks and register new ones automatically.
[1]: f73de421e2/mail_tracking/models/mail_tracking_event.py (L31-L42)
[2]: https://documentation.mailgun.com/en/latest/api-events.html#event-types
[3]: https://documentation.mailgun.com/en/latest/api-webhooks-deprecated.html
