docs: add logs and metrics page

[narcisonunez]

Adds core/logs-and-metrics.mdx, the documentation for the Logs & Metrics feature from Dokploy/dokploy#5624. The page covers:

• the supported providers and their fields
• the "Sends" selection
• adding a provider and testing its connection
• deploying the Vector agent per server from the single Servers section
• Redeploy
• the dokploy.* metadata on logs and the dokploy_* tags on metrics
• cAdvisor
• multi-organization behaviour on the Dokploy server
• Dokploy Cloud limits and troubleshooting, including the ~30 s counter delay on Datadog/CloudWatch and the cloudwatch:PutMetricData permission

It's listed in core/meta.json under Server, after Backups.

Merge this together with Dokploy/dokploy#5624, which supersedes Dokploy/dokploy#5408. This PR supersedes #196.