Restructure webhook module

[delvh]

Previously, there was an import services/webhooks inside modules/notification/webhook.
This import was removed (after fighting against many import cycles).
Additionally, modules/notification/webhook was moved to modules/webhook,
and a few structs/constants were extracted from models/webhooks to modules/webhook.

[lunny]

I think modules/webhook is a better place than modules/notification/webhook.

[KN4CK3R]

What problem does this PR solve? The notification system depends heavily on other parts of our codebase and should therefore be moved into the services packages. It's not a "module" in our definition.

[delvh]

Yes. That's also what I did with the former modules/notification/webhook/webhook.go.
That's now services/webhook/notifier.go.

---

As to what problem this PR solves
(or at least improves, it was too much too fix all flaws at once):
https://docs.gitea.io/en-us/guidelines-backend/#package-dependencies:

Since Golang don’t support import cycles, we have to decide the package dependencies carefully. There are some levels between those packages. Below is the ideal package dependencies direction.
cmd -> routers -> services -> models -> modules

So, overall, I simply untangled our way too complicated import structure slightly.
The end goal is of course to follow the guideline completely, but as you can see, this single one-line change was already so problematic that the PR to fix it changes 500 lines.

---

By the way, I can spoiler you that I opened this PR due to a comment I made on my unreleased PR review for #21937.
It also shows you why we need this change: Otherwise even new features like the actions can't be created easily anymore, because you always have to work around the import cycles, which can cost a lot of developers nerves.

[lunny]

Yes. That's also what I did with the former modules/notification/webhook/webhook.go. That's now services/webhook/notifier.go.

As to what problem this PR solves (or at least improves, it was too much too fix all flaws at once): https://docs.gitea.io/en-us/guidelines-backend/#package-dependencies:

Since Golang don’t support import cycles, we have to decide the package dependencies carefully. There are some levels between those packages. Below is the ideal package dependencies direction.
cmd -> routers -> services -> models -> modules

So, overall, I simply untangled our way too complicated import structure slightly. The end goal is of course to follow the guideline completely, but as you can see, this single one-line change was already so problematic that the PR to fix it changes 500 lines.

By the way, I can spoiler you that I opened this PR due to a comment I made on my unreleased PR review for #21937. It also shows you why we need this change: Otherwise even new features like the actions can't be created easily anymore, because you always have to work around the import cycles, which can cost a lot of developers nerves.

I think this is a right direction. notification should be kept in modules because it will be used by other services and other services could RegisterNotification so that all code have been put in the right directories. Good work!

[delvh]

Hmm, why does the CI keep failing consistently at the same location?
I didn't change any behavior, right?
Especially: Why did it work prior to the merge, and since then it complains about a failing test?
The tests are also started using main.go, right?

[zeripath]

As an aside I think notification belongs in services not modules. It clearly depends on models and therefore should be in services.

[codecov-commenter]

Codecov Report

Merging #22256 (db7db12) into main (7cc7db7) will decrease coverage by 0.56%.
The diff coverage is 45.34%.

@@            Coverage Diff             @@
##             main   #22256      +/-   ##
==========================================
- Coverage   48.15%   47.58%   -0.57%     
==========================================
  Files        1043     1044       +1     
  Lines      142324   142432     +108     
==========================================
- Hits        68536    67777     -759     
- Misses      65608    66551     +943     
+ Partials     8180     8104      -76     

Impacted Files	Coverage Δ
cmd/dump_repo.go	0.00% <ø> (ø)
models/asymkey/gpg_key.go	55.88% <0.00%> (-0.67%)	⬇️
models/asymkey/ssh_key_fingerprint.go	47.36% <0.00%> (ø)
models/asymkey/ssh_key_parse.go	59.44% <0.00%> (ø)
models/asymkey/ssh_key_principals.go	43.66% <0.00%> (ø)
models/db/context.go	63.47% <0.00%> (-1.71%)	⬇️
models/org_team.go	40.55% <0.00%> (ø)
models/packages/conan/references.go	79.31% <ø> (ø)
models/packages/container/search.go	70.40% <ø> (ø)
models/packages/package.go	50.33% <ø> (ø)
... and 196 more

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[lunny]

make L-G-T-M work