Refactor/sdk

[Avarei]

Description of your changes

This increases the actual typesafety by enforcing correct types of all Resources.
e.g. you can not set ready on composite resources and it is not available on observed composed resources.

It also makes some resourcs easier to use in practice.
e.g. instead of ready = READY_TRUE you can now specify it as ready = true

I have:

• Read and followed Crossplane's contribution process.
• Added or updated unit tests for my change.