What does this PR do?

This PR adds certain building blocks that will support the creation of new modules, and the migration of old examples to modules. For that:

• it is adding a CustomizeRequestOption type which will be used in modules as a functional opt to customize the initial container request.
• it is adding a func that modifies a container request, in order to provide our users with a way to customize the predefined container request for a given module. This function is able to merge the original request with the one provided by the users, appending maps and slices when needed.
• because we are using a library for the merge (https://github.com/imdario/mergo), we are updating the Go dependencies to all modules.
• it is also adding helper functional options for updating the Image, the WaitStrategy and the Docker types modifiers (for advanced configurations). This "sugar" represents what we consider the most used customizations from users.
• it is enriching the log output when starting a container, using emojis. We consider that this log is important to understand what image is run, and when the container is created and started.

=== RUN   TestContainerCreationWithName
Testcontainers properties file has been found: /Users/mdelapenya/.testcontainers.properties
2023/03/28 18:08:40 github.com/testcontainers/testcontainers-go - Connected to docker: 
  Server Version: 20.10.23
  API Version: 1.41
  Operating System: Docker Desktop
  Total Memory: 7851 MB
2023/03/28 18:08:40 🐳 Starting container id: 365d35ee2b6a image: docker.io/testcontainers/ryuk:0.4.0
2023/03/28 18:08:40 🚧 Waiting for container id 365d35ee2b6a image: docker.io/testcontainers/ryuk:0.4.0
2023/03/28 18:08:40 ✅ Container is ready id: 365d35ee2b6a image: docker.io/testcontainers/ryuk:0.4.0
2023/03/28 18:08:40 🐳 Starting container id: c06ec5047fb8 image: docker.io/nginx:alpine
2023/03/28 18:08:40 🚧 Waiting for container id c06ec5047fb8 image: docker.io/nginx:alpine
2023/03/28 18:08:40 ✅ Container is ready id: c06ec5047fb8 image: docker.io/nginx:alpine
    docker_test.go:2211: terminating container
--- PASS: TestContainerCreationWithName (1.13s)
PASS
ok      github.com/testcontainers/testcontainers-go     1.349s

• we are adding a guide to create modules in the docs site, including a section to migrate the legacy examples. Render URL: https://deploy-preview-1016--testcontainers-go.netlify.app/modules/
• the code generation tool will generate the scaffolding for the container options and container methods in the docs site for the module.

Why is it important?

Simplify the experience writing modules, preparing for the new Go design.