Convert samples from dotnet/extensions to doc articles

[JunTaoLuo]

We are removing samples from dotnet/extensions. In case we want to convert any of them to samples in our docs, we can find the source in the commit history: https://github.com/dotnet/extensions/tree/75759edc975749e1a8c4198c0078755a1822eac8.

After looking through them, here's my take on whether they would be valuable:

Sample	Valuable?	Notes
MemoryCacheConcurencySample	no	Seems to just illustrate mem cache can handle concurrency.
MemoryCacheFileWatchSample	no	The sample illustrate using IChangeToken from a file provider in a memory cache a file provider. Suspect API docs should be sufficient
MemoryCacheSample	no	All basic mem cache functionalities are already documented.
ProfilingSample	no	This is a terrible sample, even for illustrating profiling.
SqlServerCacheConcurencySample	no	Seems to just illustrate SqlServer cache can handle concurrency.
RedisCacheSample	no	Basic usage of Redis cache is covered in docs.
SqlServerCacheSample	no	Basic usage of SqlServer cache is covered in docs.
Logging/SampleApp	no	Basic usage of Logging is covered in docs.
HttpClientFactorySample	yes	We don't seem to have a lot of documentation regarding Polly integration, this sample could be valuable when writing a doc on this topic.
GenericHostSample	marginal	Seems like all concepts are covered by our docs at: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/generic-host?view=aspnetcore-3.1. However, there may be a few scenarios that are not explicitly illustrated in our docs such as externally controlled or windows service based generic host apps.
SampleMsmqHost	marginal	Though this is a more elaborate sample of generic host usage and illustrates the use of Msmq, it doesn't present any scenario that isn't covered by our docs.

[JunTaoLuo]

FYI @anurse @dotnet/extensions-migration