Add source plugin system

[Spazzy757]

Description

We need to have the ability to add sources to Aether for the cases of on-prem and different monitoring stacks. This will be quite a big refactor to accommodate this as we will need to figure out the factor's logic.

I propose we do this in a couple of steps:

• Define an interface for a source
• Adapt GCP providers to adhere to this interface (this essentially will have the same functionality that we currently have)
• Adapt AWS providers to adhere to this interface (this essentially will have the same functionality that we currently have)
• Adapt factors to be able to load custom data factors (bring your own data source)
• Create a plugin setup (similar to exporters) that will load sources externally

Each of the above should get its own issue and we should try make sure all changes are backwards compatible