Update to .NET 8 and merge PR fixes

features:

- [x] Google auth https://github.com/skoruba/IdentityServer4.Admin/pull/853
- [x] Update to .NET 8

fixes:

- [x] https://github.com/skoruba/IdentityServer4.Admin/pull/1055
- [x] https://github.com/skoruba/IdentityServer4.Admin/pull/1030/files
- [x] https://github.com/skoruba/IdentityServer4.Admin/pull/988
