[FEATURE] Pre-release nuget deploys when items get merged into main

**ECS integration/library project(s) (e.g. Elastic.CommonSchema.Serilog)**:
N/A
**Is your feature request related to a problem? Please describe.**
A feature just merged which fixes a problem for me #327
While it was merged into master a pipeline ran to create some packages, but they haven't been uploaded to nuget.org

**Describe the solution you'd like**
nuget.org does support pre-releases, beta, release-candidates etc as so does GH actions would it be possible to do this for merges into main?

**Describe alternatives you've considered**
Couldn't think of any.