Add caching to .NET installation in our pipelines

The [`azure-sdk-for-net install-dotnet.yml`](https://github.com/Azure/azure-sdk-for-net/blob/main/eng/pipelines/templates/steps/install-dotnet.yml) appears to [support caching](https://github.com/Azure/azure-sdk-for-net/blob/7c5937cdc7c02e2787244c1703c95936d97a7130/eng/pipelines/templates/steps/install-dotnet.yml#L29-L35). [`azure-sdk-tools install-dotnet.yml`](https://github.com/Azure/azure-sdk-tools/blob/main/eng/pipelines/templates/steps/install-dotnet.yml) does not as of now. Ideally, it should.

Relevant docs:

- https://learn.microsoft.com/en-us/azure/devops/pipelines/release/caching?view=azure-devops
- https://learn.microsoft.com/en-us/azure/devops/pipelines/artifacts/caching-nuget?view=azure-devops
- https://learn.microsoft.com/en-us/azure/devops/pipelines/tasks/reference/cache-v2?view=azure-pipelines