Setup folder structure to store artifact configurations

[minherz]

Description

All Configurations are stored under /configurations folder at the root of the repo. Each Configuration is stored in a dedicated folder. The name of the folder is used as ID of the configuration. The name is validated by regex ^[a-zA-Z_][a-z-A-Z0-9_\-]+$ (letters, numbers, underscore and dash, starting with a letter or underscore with the length greater than 1).

Inside each Configuration the parameters are stored in multiple files per artifact functionality:

• alerts.yaml -- alert policies and notification channels
• dashboards.yaml -- custom monitoring dashboards
• healthchecks.yaml -- health check definitions
• metrics.yaml -- custom log-based metric definitions
• services.yaml -- custom monitoring service definitions
• slos.yaml -- monitored service SLOs including custom and auto-recognized services

Additionally, the folder will has a recipe subfolder /configurations/{ID}/recipes to store o11y recipes (see #1028)

Schemas for these YAML files will be stored in the /provisioning/schemas/configuration folder.

Describe alternatives you've considered

The following options were considered:

• each Configuration is stored in a single file that describes ALL artifacts
  pros simple to transfer and host
  cons hard to manage or even understand because the file will be too big
• use index file to describe a Configuration; artifacts can be referenced as independent files stored anywhere
  pros flexible storage options
  pros allows artifact parameters across multiple files (e.g. two files to store service SLOs)
  pros allows reuse configurations
  cons hard to host and transfer; increases chances to cause unexpected problems when modifying a file referenced in more than one Configuration
  cons hard to manage or even understand because the files can be distributed and parameters can conflict

Additional context

It is a sub-issue for #1026.