Add options to createPresignedRequest method

[clauculo]

*Issue: None

Description of changes:
This tiny change will make it possible to sign pre-signed-requests with optional parameters, this can be used to make use of this part of the code:

aws-sdk-php/src/Signature/SignatureV4.php

Lines 169 to 171 in 7254925

	$startTimestamp = isset($options['start_time'])
	? $this->convertToTimestamp($options['start_time'], null)
	: time();

This wil make it possible to sign the S3 links with a timestamp in the past!
This is very handy if you want to make use of short caching.
Without the options, every signed url will have an unique signature, because time() function is used.

Found here:
https://github.com/clauculo/aws-sdk-php/blob/725492580ef8a49108e39803dc266c25faa30d5a/src/Signature/SignatureV4.php#L171

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