Add social icon for Threads

[geeqla]

What does this PR change? What problem does it solve?

Hello @adityatelange

Added a social icon for Threads (all-new social media app by Meta).

Logo: https://en.wikipedia.org/wiki/Threads_%28app%29

Usage:

socialIcons:
  - name: threads
     url: "https://www.threads.net"

Live preview: https://www.geeqla.com (works for both "dark" and "light" themes)

Also, made a few tiny (cosmetic) changes:

• Removed line break above the "telegram" icon
• Added extra tab for the "tumblr" icon

Was the change discussed in an issue or in the Discussions before?

No.

PR Checklist

• This change adds/updates translations and I have used the template present here.
• I have enabled maintainer edits for this PR.
• I have verified that the code works as described/as intended.
• This change adds a Social Icon which has a permissive license to use it.
• This change does not include any CDN resources/links.
• This change does not include any unrelated scripts such as bash and python scripts.
• This change updates the overridden internal templates from HUGO's repository.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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