Resilience dependencies for ORAS

[sajayantony]

Enabling a good foundation, as this library matures and as we add more resilience capabilities to this like #49, would be critical to the long term usage.

With that in mind and having had some discussions internally with folks like @kichalla and @nathana1, I would like to propose we align with dotnet 8.0 which is LTS and has good alignment with Polly.

The main advantages I see are that we consider things like retries and resiliency from the get-go before we create an auth model. This also enables investing in testing as well.

The downsides, which all choices usually have, are that we have a larger dependency footprint. However, the fact remains that we create a library that can someday be used in serious application and not just for a sample or demo.

Thoughts? @shizhMSFT @Wwwsylvia

[shizhMSFT]

Sounds a good idea. According to the official .NET doc, new libraries should target net8.0.

[shizhMSFT]

Closed by #75