Fix https://github.com/go-gitea/gitea/pull/23894#discussion_r1573718690

In PR #26786, the Go version for golangci-lint is bumped to 1.21. This
causes the following error:

```
models/migrations/v1_16/v210.go:132:23: SA1019: elliptic.Marshal has been deprecated since Go 1.21: for ECDH, use the crypto/ecdh package. This function returns an encoding equivalent to that of PublicKey.Bytes in crypto/ecdh. (staticcheck)
                                        PublicKey:       elliptic.Marshal(elliptic.P256(), parsed.PubKey.X, parsed.PubKey.Y),
```

The change now uses [func (*PublicKey)
ECDH](https://pkg.go.dev/crypto/ecdsa#PublicKey.ECDH), which is added in
Go 1.20.

The xorm `Sync2` has already been deprecated in favor of `Sync`,
so let's do the same inside the Gitea codebase.

Command used to replace everything:
```sh
for i in $(ag Sync2 --files-with-matches); do vim $i -c ':%sno/Sync2/Sync/g' -c ':wq'; done
```

Change all license headers to comply with REUSE specification.

Fix #16132

Co-authored-by: flynnnnnnnnnn <flynnnnnnnnnn@github>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>

There are too many files in `models/migrations` folder so that I split
them into sub folders.

Found using
`find . -type f -name '*.go' -print -exec vim {} -c
':%s/fmt\.Errorf(\(.*\)%v\(.*\)err/fmt.Errorf(\1%w\2err/g' -c ':wq' \;`

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

* Update the webauthn_credential_id_sequence in Postgres

There is (yet) another problem with v210 in that Postgres will silently allow preset
ID insertions ... but it will not update the sequence value.

This PR simply adds a little step to the end of the v210 migration to update the
sequence number.

Users who have already migrated who find that they cannot insert new
webauthn_credentials into the DB can either run:

```bash
gitea doctor recreate-table webauthn_credential
```

or

```bash
./gitea doctor --run=check-db-consistency --fix
```

which will fix the bad sequence.

Fix #19012

Signed-off-by: Andrew Thornton <art27@cantab.net>

We can't depend on `latest` version of gofumpt because the output will
not be stable across versions. Lock it down to the latest version
released yesterday and run it again.

v208.go is seriously broken as it misses an ID() check. We need to no-op and remigrate all of the u2f keys.

See #18756

Signed-off-by: Andrew Thornton <art27@cantab.net>

Unfortunately credentialIDs in u2f are 255 bytes long which with base32 encoding
becomes 408 bytes. The default size of a xorm string field is only a VARCHAR(255)

This problem is not apparent on SQLite because strings get mapped to TEXT there.

Fix #18727

Signed-off-by: Andrew Thornton <art27@cantab.net>