Update Azure Blob SDK and cleanup

[JimBobSquarePants]

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

• Updates the Azure SDK to the latest version.
• No longer attempts to create a container when none exists. (Don't throw, just let Azure throw)
• Removes all unneeded ConfigureAwait(false) calls.

[codecov]

Codecov Report

Merging #87 into master will increase coverage by 0.25%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##           master      #87      +/-   ##
==========================================
+ Coverage   76.39%   76.65%   +0.25%     
==========================================
  Files          47       47              
  Lines        1322     1311      -11     
  Branches      230      229       -1     
==========================================
- Hits         1010     1005       -5     
+ Misses        242      238       -4     
+ Partials       70       68       -2

Flag	Coverage Δ
#unittests	76.65% <71.42%> (+0.25%)	⬆️

Impacted Files	Coverage Δ
.../Providers/AzureBlobStorageImageProviderOptions.cs	100% <ø> (+33.33%)	⬆️
src/ImageSharp.Web/Caching/AsyncKeyLock.cs	100% <100%> (ø)	⬆️
src/ImageSharp.Web/Middleware/ImageContext.cs	72.41% <100%> (ø)	⬆️
.../ImageSharp.Web/Caching/PhysicalFileSystemCache.cs	94.23% <100%> (+1.92%)	⬆️
src/ImageSharp.Web/ImageCacheMetadata.cs	80% <100%> (+1.81%)	⬆️
.../ImageSharp.Web/Middleware/ImageSharpMiddleware.cs	73.28% <57.89%> (-0.19%)	⬇️
...s.Azure/Providers/AzureBlobStorageImageProvider.cs	80% <66.66%> (+3.52%)	⬆️
...s.Azure/Resolvers/AzureBlobStorageImageResolver.cs	90% <75%> (ø)	⬆️

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