Updated the KeyExists from aws to keep the response metadata in the image resolver

[mdupras]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

When the image is resolved we validate if it exists with the method KeyExists. To validate this the methods fetch all the object metadata, if it fails it's considered not existent, but the result of that query isn't used.
This PR keeps the result and pass it to the AWS S3 image resolver.
I added an optional parameter for that metadata, in case the resolver needs to be build it elsewhere. If the metadata is not provided, it will fetch it like it used to.

Since I had overlapped change with #312, I included the change of those files in my PR to limit the conflicts and use the nullable options ;)

[codecov]

Codecov Report

Merging #317 (2acb001) into main (fb8b334) will decrease coverage by 1%.
The diff coverage is 64%.

@@         Coverage Diff         @@
##           main   #317   +/-   ##
===================================
- Coverage    85%    85%   -1%     
===================================
  Files        77     77           
  Lines      2195   2195           
  Branches    308    309    +1     
===================================
- Hits       1876   1873    -3     
- Misses      231    233    +2     
- Partials     88     89    +1     

Flag	Coverage Δ
unittests	85% <64%> (-1%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...oviders.AWS/Providers/AWSS3StorageImageProvider.cs	66% <63%> (-1%)	⬇️
...oviders.AWS/Resolvers/AWSS3StorageImageResolver.cs	92% <66%> (-8%)	⬇️

... and 1 file with indirect coverage changes

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[JimBobSquarePants]

HI @mdupras thanks for this.

Would it be possible to revert the nullability changes since they overlap with the other PR which will actually increase the probability of conflicts since there have been changes requested there?

[mdupras]

HI @mdupras thanks for this.

Would it be possible to revert the nullability changes since they overlap with the other PR which will actually increase the probability of conflicts since there have been changes requested there?

Yea no problem! Just did it!

[JimBobSquarePants]

Lovely stuff. Thanks!