New variable for cache s3 bucket (for reuse)

[ivanmartos]

Describe the Feature

Currently when s3 cache is requested, module will create new s3 bucket. Idea is about providing s3 bucket that will be used for caching instead of creating new one

Expected Behavior

Add an optional variable s3_cache_bucket_name that will contain name of the s3 bucket to be used for caching. If s3 cache will be requested and this var will not be provided create new s3 bucket as is currently implemented. Otherwise use this s3 bucket and add required iam policy

Use Case

number of s3 buckets is limited so it makes sense to reuse them