PC-10133: Move api models to separate package

[nieomylnieja]

API models which are not part of our IaC managed objects (SLO, Service etc.) but are simply payloads used to create and read requests to our HTTP API should be moved to a more appropriate location. Since they are directly tied to sdk.Client and its methods and don't serve any purpose outside of sdk.Client scope, they should be moved to sdk package, into a sub-package called models.

These models include:

• Replay models
• SLI Analysis models
• SLO Status API models

Currently Replay models have been moved to models pkg as a role model. SLI Analysis has been moved to n9 as it does not contain all the models for all analysis endpoints.

To accommodate the changes and further polish up the validation package several major changes were introduced:

• rename refactor to better align the API with Fluent Validation and hopefully make things clearer to read too
• ability to include validators with Include keyword in property rules, it also results in a parent property path/name being prepended to its children
• new validators (comparable and required)
• added error codes concept, these are currently mostly used to ease up the testing process, since you do not to rely on checking the message (which is dynamic often times)
• added flow execution mechanism in form of StopOnError
• each of Rules, When, Include and StopOnError is executed sequentially, order of steps matters!