Add a dependencies.prop file for the library

> Please provide us with the following information:
> ---------------------------------------------------------------

### This issue is for a: (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [x] feature request
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

A common practice is to have a 'dependencies.prop' file that defines the dependencies version.
For example the file would contain:
3.0.3

Then TodoListService.csproj would include dependencies.prop and write:

This makes updating versions simpler and the same across projects.
For example see:
https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/blob/dev5x/build/dependencies.props

https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/blob/dev5x/src/Microsoft.IdentityModel.Tokens/Microsoft.IdentityModel.Tokens.csproj

Start by locating TodoListService.csproj and reviewing its existing PackageReference entries. Add the requested dependencies.prop file and update the project references so dependency versions are centralized there; done means the project still restores and builds with the shared version properties.

Written by the indexing model from the issue text.