Support populating Hub manifests from multiple sources

[mszostok]

Description

Add support in populator for multiple manifests sources.

Currently, we process manifests only from one location, see:

capact/deploy/kubernetes/charts/capact/charts/hub-public/values.yaml

Lines 82 to 86 in 9da725c

	manifestsLocation:
	local: false
	# It's public repository
	repository: github.com/capactio/hub-manifests
	branch: main

This should be change to a list of locations. This simply approach enables basic feature of federation where manifests can be split across different location as described here: #511

This task doesn't replace or invalidate the need for federation, and it still needs to be implemented.

• Simple behavior: Return error in case of manifest conflicts
• Include documentation on capactio/website
• Reorganize hub manifest repositories if necessary

Reason

In the current approach, all content that is loaded to Public Hub requires to be defined in a single repository. There is no easy way to split it e.g. extract test content to separate och repository which can be optionally enabled.

This pattern doesn't scale well. We need to enable an option to split manifests across different location but don't need a proper federation yet.

Use cases

• System User - has an option to enable only those manifests that are needed. Doesn't need to create an umbrella repository, to use manifest from different location.
• Content Developer - doesn't need to put all created manifests in a single location.