Update cpp-stl-cheatsheet.md with pair sorting

[LegendaryGene]

What does this PR do?

Add content(s)

Description

Added sorting by first and second element in cpp pair

Additional context

Uses internal quicksort implementation for sorting

Checklist:

• [x] Read our contributing guidelines.
• [x] Search for duplicates.
• [x] Used an informative name for this pull request.

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[LegendaryGene]

Please Merge this so I can get the HacktoberFest submission @crescentpartha

[LegendaryGene]

Done, now please do @crescentpartha