chore(databases): update mongodb version, to patch latest cve

[stripsior]

What is this PR about?

This pull request updates default Docker image versions for database services, ensuring consistency and using more recent versions where appropriate.

Database Docker image version updates:

• Updated the default Docker image placeholder for MongoDB from mongo:7 to mongo:8 in the dockerImageDefaultPlaceholder mapping in add-database.tsx.
• Set the default value for the dockerImage field to mariadb:8 in the mariadb schema, replacing the previous requirement for explicit specification.

Checklist

Before submitting this PR, please make sure that:

• You created a dedicated branch based on the canary branch.
• You have read the suggestions in the CONTRIBUTING.md file https://github.com/Dokploy/dokploy/blob/canary/CONTRIBUTING.md#pull-request
• You have tested this PR in your local instance.

[stripsior]

I read wrong, and edited mariadb version not mongodb in schema files. Fixed

[gOOvER]

there is no direct way to upgrade from 7x to 8.2. If there is any existing Database, it will fail and destroy the database

[stripsior]

Existing databases shouldn't be affected by that change, as I only changed default values for new deployments. This will provide safe way of creating new mongodb instances