doc: update JSDoc for tempConversion.js

[Fai]

Hello, please let me know how to improve if any as this is my first hacktoberfest commit :D

I added JSDoc comments to improve code documentation.

This pull request adds JSDoc comments to the tempConversion.js file to improve the documentation of the code. The JSDoc comments provide information about the input and output types of each function, as well as their purpose and behavior.

The JSDoc comments were added to the following functions:

• identityFunction
• celsiusToFahrenheit
• celsiusToKelvin
• celsiusToRankine
• fahrenheitToCelsius
• fahrenheitToKelvin
• fahrenheitToRankine
• kelvinToCelsius
• kelvinToFahrenheit
• kelvinToRankine
• rankineToCelsius
• rankineToFahrenheit
• rankineToKelvin
• tempFunctionMap
• tempUnitMap

The JSDoc comments follow the standard format for documenting JavaScript code and provide useful information for developers who need to work with this code in the future.

Please review and merge this pull request if you find it satisfactory.

Thank you!

[gits-up]

Good work

[Fai]

I'm very sorry to disturb you but seems like Hacktoberfest doesn't count this PR, could your please add the other labels for hacktoberfest to make it count on the site, i would be really appreciate that, Thank you @gits-up