adding Dapr Repository Index for contributing

[AnnuCode]

Thank you for helping make the Dapr documentation better!

Please follow this checklist before submitting:

• [x] Commits are signed with Developer Certificate of Origin (DCO - learn more)
• [x] Read the contribution guide
• [ ] Commands include options for Linux, MacOS, and Windows within codetabs
• [ ] New file and folder names are globally unique
• [x] Page references use shortcodes instead of markdown or URL links
• [ ] Images use HTML style and have alternative text
• [ ] Places where multiple code/command options are given have codetabs

In addition, please fill out the following to help reviewers understand this pull request:

Description

Added an index list of Dapr repositories to facilitate users interested in contributing.

Issue reference

Fixes #4076

[github-actions[bot]]

Stale PR, paging all reviewers

[marcduiker]

@holopin-bot @AnnuCode Thanks Annu! 😁

[holopin-bot[bot]]

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