Added a submitting class for cmp-adaptiveform-container

[armaang1729]

Description

Added a separate CSS class .cmp-adaptiveform-container--submitting to display a loader when the form is being submitted.

Related Issue

Currently, the form can be submitted multiple times if the user clicks the submit button repeatedly before the first request finishes.
To address this, we introduced a loader (similar to the one shown at form rendering) that disables further duplicate submissions.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.