feat(backups): add a native MongoDB (psmdb) backup-strategy driver #3545

Summary

The backup-strategy framework (backups.cozystack.io + strategy.backups.cozystack.io)
ships native drivers for Postgres (CNPG), MariaDB (MariaDB), ClickHouse
(Altinity), Etcd (Etcd), FoundationDB (FoundationDB), plus the generic
Velero and Job strategies. MongoDB has no native driver, even though
cozystack ships the Percona psmdb operator, which provides its own
PerconaServerMongoDBBackup / PerconaServerMongoDBRestore CRDs.

As a result a managed MongoDB app can only be backed up either:

• via the Velero strategy — a crash-consistent PVC snapshot at the app level; or
• via a hand-written generic Job strategy running mongodump.

There is no logical, engine-native backup through the unified
BackupJob / RestoreJob API, and therefore no PITR and no
restore-into-a-differently-named instance (both of which the native DB drivers
like CNPG provide).

Current state

• No mongodbs.strategy.backups.cozystack.io kind. The BackupJob / RestoreJob
  dispatch handles only Job, Velero, CNPG, Altinity, MariaDB,
  FoundationDB, Etcd.
• cozy-default BackupClass has no MongoDB mapping.
• The shipped psmdb operator already exposes
  PerconaServerMongoDBBackup / PerconaServerMongoDBRestore, which a driver
  could orchestrate — analogous to the CNPG driver wrapping
  cnpg.io/Backup, MariaDB wrapping the mariadb-operator, and Altinity
  wrapping clickhouse-backup.

Why it matters

MongoDB is offered as a managed application, but its backup story is
inconsistent with the other managed databases: users get only crash-consistent
PVC snapshots or must build and maintain their own mongodump Job strategy.
There is no declarative, engine-native path and no point-in-time / cross-instance
restore.

Proposal

• Add a MongoDB backup-strategy driver (e.g. kind MongoDB under
  strategy.backups.cozystack.io) that drives the psmdb operator's
  PerconaServerMongoDBBackup / PerconaServerMongoDBRestore.
• Wire it into the BackupJob / RestoreJob dispatch and the supported-kinds
  list.
• Add a Postgres-style MongoDB mapping to the cozy-default BackupClass.