datasource(dotnet-version): use the release_date as releaseTimestamp

[RahulGautamSingh]

Describe the proposed change(s).

The dotnet-version first fetches all the available channels (major version) from the https://dotnetcli.blob.core.windows.net/dotnet/release-metadata/releases-index.json url.
Example
This reponse returns a json object, which contains the list of all channels, and links which can be used to fetch the versions available for each.

We then fetch the releases for each channel using that link. In this response along with other information there is the release_date field, which can be used as the releaseTimestamp.
Example

[RahulGautamSingh]

False flag!

This datasource returns releaseTimestamp field. I missed it because I only checked the tests and they didn't include them. But when I checked the schema, it was clear that they were being returned, just not tested.

I will modify the tests instead to include the releaseTimestamp field.