feat: [FC-0047] move the certificate view from the banner to the message section

[volodymyr-chekyrta]

This PR is related to the FC-0047 course home redesign and includes the new certificate message block.

Design:
https://www.figma.com/design/iZ56YMjbRMShCCDxqrqRrR/Open-edX-Mobile-App-All-Screens-v2.1?node-id=14957-309221&t=e1C9Uxns0YlV3sHh-0

Demo:

Phone	Tablet

Changes:

• Introduced new composable function CourseMessage.
• Removed unused CourseImageHeader and string resources.

Checklist:
✅ Certificate message appears if the course certificate is earned
✅ A11y. The message block has a big clickable area and works as 1 object for the TalkBack

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[volodymyr-chekyrta]

@HamzaIsrar12 @k1rill, Kindly review the changes made in this pull request. Thank you.

[HamzaIsrar12]

One minor nit only. 👍🏻

[HamzaIsrar12]

LGTM 🏎️

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