Update module yaml to v2.4.0

See merge request !5

Update module go-sql-driver/mysql to v1.5.0

See merge request !4

Update module lib/pq to v1

See merge request !7

Configure Renovate

See merge request !3

Add specific instrumentation for Keystore operations

See merge request !2

The messages should look less confusing now, as the phrasing for
expected errors has been changed.

This makes it easier to detect unexpected errors.

Add SQL support

See merge request !1

Introduces the "sql" backend, and refactors backends behind a nicer
interface (which looks a lot like the one in id/auth). Users can
define arbitrary SQL queries to fetch the key data, to adapt to their
database schema.

Include vendored dependencies for sqlite3/mysql/postgres.

Avoid implementing our own version of asp/userenckey/u2f serialization
and deserialization.

Sets 'noauthenticate', and prefixes the private key with the userdb_
prefix as it should.

And upgrade dependencies.