Add alphabetical contact grouping and sectioning

[mawalou14]

Closes: #992

• Title: Organize Contacts Alphabetically with Section Separators ( Contact Manager App)
• Name: Mouhamadou Awalou
• Idenitfy yourself: Hacktoberfest Contributor

Describe the add-ons or changes you've made 📃

• Implemented alphabetical grouping of contacts.
• Added section headers (A-Z) to indicate contact groups.
• Updated the search functionality to ensure it filters across all sections accurately.
• Sorted the contact list in ascending alphabetical order.
• Updated the screnshot.webp file and the images reflecting the new changes.

Screenshots 📷

Type of change ☑️

What sort of change have you made:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [x] Code style update (formatting, local variables)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Checklist: ☑️

• [x] My code follows the Contributing Guidelines & Code of Conduct of this project.
• [x] This PR does not contain plagiarized content.
• [x] I have performed a self-review of my own code.
• [x] I have commented my code, particularly wherever it was hard to understand.
• [x] My changes generate no new warnings.

Note to reviewers 📄

Thanks @Avdhesh-Varshney, let me know if any further adjustments are required.

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