(docs) improvement of the agent installation in Docker

[prashant-shahi]

Summary

We recently shipped Infra Agent for Docker and Swarm as part of the OSS improvement epic task.

We need the instructions from Set Up Infra Agent under the install page to an independent guide page as well.

• https://signoz.io/docs/install/docker/#set-up-infra-agent
• https://signoz.io/docs/install/docker-swarm/#set-up-infra-agent

Additional Contexts

Point 3 from this: https://www.reddit.com/r/opensource/comments/1haaj5g/comment/mea6d1i/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button