[Feat]: Make the add nodes to room button easier to see/use

[shyamvalsan]

Problem

When creating a new room and selecting nodes to be added to it. The add nodes button appears greyed out and is hard to notice for new users.

Description

https://github.com/netdata/netdata-cloud/assets/24860547/50abacf4-82ef-438a-b4d9-bcd9d2ad4604

Importance

must have

Value proposition

1. Make it easier to add more nodes to more rooms

Proposed implementation

Maybe on selecting nodes there is a Add Nodes green button that appears or something.