fix(Integration): Incoming webhook 'Emoji filed 'has no validation

Description:

When Creating a new incoming webhook the Emoji Filed dosent have proper validation ex:[ ghost ] it will taking this as emoji field . but under the text box clearly mentioned that it should start and end with colon

Steps to reproduce:

1.Navigate the Adminstration click on the Integration
2. click on the new tab
3. select the Incoming tab
4. Fill in all required fields (e.g., Name: Test Emoji, Post to Channel: #general, Post as: Kalyan12).
5. Scroll down to the "Avatar URL" field.
6.Type an invalid string that is not a Emoji type string (e.g., ghost ).
7.click on save button

Expected behavior:

If the user tries to fill the Emoji field .The form should not be save. Because the value provided, should not be validated .It should throw an error should appear like "please enter an valid emoji name"

Actual behavior:

The form saves successfully with the invalid string in the "Emoji String" field. A green "Integration has been saved" toast message appears, and the integration is created with a broken Emoji String.

Server Setup Information:

• Version of Rocket.Chat Server: develop(running in local development
• License Type:community
• Number of Users: 1
• Operating System: ubuntu(via WSL)
• NodeJS Version: 22.16.0
• MongoDB Version:6.10.0

Client Setup Information

• Desktop App or Browser Version:chrome(latest)
• Operating System:Windows

Relevant logs:

No server or console logs are generated because the application incorrectly treats this as a successful operation. The bug is the absence of a validation error.

Start at Administration > Integrations > Incoming webhook and reproduce the issue by entering an invalid value such as "ghost" in the Emoji String field. Trace the incoming webhook form's validation and save flow; done means invalid emoji names are rejected with a validation error and the integration is not saved.