update nuget package and adapt dockerfile to .net 6 (#639)

src/PublicApi/Dockerfile

@@ -1,11 +1,11 @@
 #See https://aka.ms/containerfastmode to understand how Visual Studio uses this Dockerfile to build your images for faster debugging.
 
-FROM mcr.microsoft.com/dotnet/aspnet:5.0-buster-slim AS base
+FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS base
 WORKDIR /app
 EXPOSE 80
 EXPOSE 443
 
-FROM mcr.microsoft.com/dotnet/sdk:5.0-buster-slim AS build
+FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
 WORKDIR /app
 COPY . .
 #COPY ["src/PublicApi/PublicApi.csproj", "./PublicApi/"]