[Docs]: Custom session timeout

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Engineering Ticket Link

https://github.com/appsmithorg/appsmith/issues/24455

### Release Date

Released in v1.18

### Release Number

v1.18

### First Draft

_No response_

### Loom video

_No response_

### Discord/slack/intercom Link if needed

_No response_

### PRD

_No response_

### Test plan/cases

_No response_

### Use cases or user requests

This is a minor edit where we're now supporting custom session timeouts for Enterprise customers. The ticket is [here](https://github.com/appsmithorg/appsmith/issues/24455) and the Slack conversation is [here](https://theappsmith.slack.com/archives/CNQ9Q91C0/p1709009235130119).

Please check with @abhvsn for any technical inputs for documentation.