feat: Implement database schema, relationships and models for survey application

- Designed an ERD (Entity-Relationship Diagram) for the survey system.
- Defined entities: User, Survey, Question, Choice, Response, and Answer.
- Established relationships:
  - Users can author multiple surveys.
  - Surveys contain multiple questions.
  - Questions have multiple choices.
  - Surveys can have multiple responses from participants.
  - Responses are linked to answers, questions, and choices.
- Ensured compliance with best practices for relational database design.
Note : no migration yet

survey-beta/Program.cs

@@ -0,0 +1,23 @@
+using Microsoft.EntityFrameworkCore;
+using survey_beta.DataBaseContext;
+
+var builder = WebApplication.CreateBuilder(args);
+
+// Add services to the container
+builder.Services.AddDbContext<AppDbContext>(options =>
+    options.UseNpgsql(builder.Configuration.GetConnectionString("DefaultConnection")));
+
+builder.Services.AddControllers(); 
+builder.Services.AddEndpointsApiExplorer(); 
+
+var app = builder.Build();
+
+// Configure the HTTP request pipeline.
+
+app.UseHttpsRedirection();
+
+app.UseAuthorization();
+
+app.MapControllers();
+
+app.Run();