[IMPROVEMENT] 'New Message' text should be greyed out

[ArchdukeTim]

Description:

In the rocket chat iOS app, the 'New Message' placeholder text is the same color as regular text, making it hard to distinguish as a placeholder. The text should be greyed out, similar to the desktop app.

Environment Information:

• Rocket.Chat Server Version: 3.9.4
• Rocket.Chat App Version: 3.12.1
• Device Name: iPhone 11
• OS Version: iOS 14

Expected behavior:

Placeholder text has different text color than regular text

Actual behavior:

Placeholder text color is the same as regular text