Generic collection for CLMS layers

[blaz-pavlica]

We added a proposal for a generic clms collection following stac collection standard. The following points should be considered:

• Summaries contain the more frequent properties
• We added the proj:shape field to the summaries, do you think it should be included?
• The links section is missing the links to the items
• assets and item_assets were not included because this is a generic collection

We would appreciate any considerations you might have and to discuss changes.

[blaz-pavlica]

@j-musial Please check our proposal.