Partially backport #32473. LFS related changes are not in 1.22, so skip
them.
1. Ignore non-existing repos during migrations
2. Improve ReadBatchLine's comment
3. Use `X-Gitea-Internal-Auth` header for internal API calls and make
the comparing constant time (it wasn't a serous problem because in a
real world it's nearly impossible to timing-attack the token, but indeed
security related and good to fix and backport)
4. Fix route mock nil check
Fix the bug on try.gitea.io
```log
2023/09/18 01:48:41 ...ations/migrations.go:635:Migrate() [I] Migration[276]: Add RemoteAddress to mirrors
2023/09/18 01:48:41 routers/common/db.go:34:InitDBEngine() [E] ORM engine initialization attempt #7/10 failed. Error: migrate: migration[276]: Add RemoteAddress to mirrors failed: exit status 128 - fatal: not a git repository (or any parent up to mount point /)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
- fatal: not a git repository (or any parent up to mount point /)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
```
Caused by #26952
---------
Co-authored-by: Jason Song <i@wolfogre.com>
This PR adds a new field `RemoteAddress` to both mirror types which
contains the sanitized remote address for easier (database) access to
that information. Will be used in the audit PR if merged.
