added getScheme() implementation in PrestoS3FileSystem.java

[pratyakshsharma]

Details in https://github.com/prestodb/presto/issues/18166

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* added getScheme() method in PrestoS3FileSystem.
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[pratyakshsharma]

@imjalpreet Can you please take the first pass here?

[pratyakshsharma]

@tdcmeehan please have a look. Let us merge this once you approve.

[pratyakshsharma]

@tdcmeehan ping!

[ajaygeorge]

@pratyakshsharma Can you fix the commit message to be in imperative mood. something like Add getScheme implementation in PrestoS3FileSystem See https://cbea.ms/git-commit/