Some NuGet package enhancements (#30280)

Some NuGet package enhancements (#30280)

Fixes #30265

1. Read second type of dependencies
2. Render `Description` and `ReleaseNotes`

old:

![grafik](https://github.com/go-gitea/gitea/assets/1666336/abac057c-11cd-4d25-b196-01ff899d948e)

new:

![grafik](https://github.com/go-gitea/gitea/assets/1666336/35302273-740c-481a-a031-1f80d2d7d336)

The NuGet spec does not specify what kind of text can be stored in the
description but we can best guess markdown. The official NuGet registry
just [converts the newlines to html
lines](https://www.nuget.org/packages/rb.Firefox#readme-body-tab).

3. Extract and render the readme. This is the new and better place to
store larger text than in the description. The content is markdown.

![grafik](https://github.com/go-gitea/gitea/assets/1666336/f442264e-3735-4b55-92c4-3b89a8ebafb0)

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Co-authored-by: Benjamin Heemann <benjamin.heemann@raith.de>