[Docs]: Clarify SSH instructions for launching Appsmith using the AMI

[alex-a-pereira]

Is there an existing issue for this?

• [X] I have searched the existing issues

Documentation Link

https://docs.appsmith.com/getting-started/setup/installation-guides/aws-ami#login-with-root-admin

Discord/slack/intercom Link

No response

Describe the problem and improvement.

When reviewing the AWS AMI self hosting documentation, it lacks specific instructions on how to SSH into the server:

• how to use the keypair generated for the EC2 instance
• which username to use in the SSH command (some AWS users might assume ec2-user if they've only used Amazon Linux)

Additionally, notes on security groups are sparse and may lead users to leave port 22 open to the internet.

I'd suggest the following changes:

• instructions on how to use the SSH keypair generated for Appsmith
• example of the SSH command used (includes using alternate private key, correct username)
• give example of security group rule for SSH access, limited to a single IP address

[jnikhila]

@pratapaprasanna and @sharat87 - FYI and providing details.