fix(avatar): use sha256 and inline the federated avatar lookup (#38843)

- Hash emails with sha256. Gravatar moved to sha256, and both it and
libravatar.org serve the same image for either hash.
- Drop `strk.kbt.io/projects/go/libravatar` for a 46 line inline SRV
lookup. It could not bound or cancel its DNS query and panicked on an
unexpected resolver error. The replacement carries the request context
and a 3s timeout.
- Fix federated avatars querying DNS for every avatar on every render.
`loadAvatarSetting` compared a cache field that was never assigned, so
each call rebuilt the resolver and dropped its cache. That cache is
gone, both settings are read where they are used.
- Migration 348 recreates `email_hash` with a 64 char hash column and a
`hash_type` column, so a later algorithm change can tell old rows apart.
The MD5 rows are unreachable and their `UNIQUE` email index would reject
the SHA256 replacements.
- Fix a re-saved avatar form replacing an uploaded avatar with a random
one.
- Remove the `duoshuo` `GRAVATAR_SOURCE` alias, that service shut down
in 2017.
- Remove dead i18n key.

Fixes: https://github.com/go-gitea/gitea/issues/34284
Fixes: https://github.com/go-gitea/gitea/issues/28110
Docs: https://gitea.com/gitea/docs/pulls/499
Signed-off-by: silverwind <me@silverwind.io>

routers/web/user/setting/profile.go

@@ -14,7 +14,6 @@ import (
 	"path/filepath"
 	"strings"
 
-	"gitea.dev/models/avatars"
 	"gitea.dev/models/db"
 	"gitea.dev/models/organization"
 	repo_model "gitea.dev/models/repo"
@@ -127,11 +126,7 @@ func ProfilePost(ctx *context.Context) {
 func UpdateAvatarSetting(ctx *context.Context, form *forms.AvatarForm, ctxUser *user_model.User) error {
 	ctxUser.UseCustomAvatar = form.Source == forms.AvatarLocal
 	if len(form.Gravatar) > 0 {
-		if form.Avatar != nil {
-			ctxUser.Avatar = avatars.HashEmail(form.Gravatar)
-		} else {
-			ctxUser.Avatar = ""
-		}
+		ctxUser.Avatar = "" // UploadAvatar sets the real storage path when a file is uploaded
 		ctxUser.AvatarEmail = form.Gravatar
 	}