Improve and extend OCM Specification

[In-Ko]

Description
The official OCM Specification needs to be improved and extended. This includes:

• Working on the leftovers, maintained at https://github.com/gardener/ocm-spec/blob/main/doc/proposal/leftovers.md, which are partially already discussed improvements, which should be integrated into the Spec, and partially also things which need discussion and agreement within the team, and after that also integration into the spec itself.
• Add further ToDos to this list (which are actively being discussed in various places like Slack, GitHub Discussions). We need a central place where to capture all leftovers / ToDos / Improvements for the OCM Spec. Let's agree on one and maintain everything there.
• Think about a possible restructuring of the Spec, to make it easily consumable. This should include a Specification Schema Browser". A good example can be found here: https://cyclonedx.org/docs/1.4/json/#bomFormat
• Finally, move from "proposal state" to real, official spec

Done Criteria

• Structure and current WiP-State of OCM Spec has been shared with everyone
• initial onboarding towards specification work (suggestion: organise a 1hr meeting)
• Leftovers and further ToDos have been discussed and integrated into the Specification, at least all of these have been added to https://github.com/gardener/ocm-spec/blob/main/doc/proposal/leftovers.md, to have a central place where we gather them all
• Proposal for a possible restructuring of the OCM Spec has been communicated and if agreed by everyone, also integrated into the OCM Spec
• After all of the above is done, the Spec is moved from "proposal" to an official place

[In-Ko]

Initial discussions about pain points in the existing OCM spec proposal started here: #15. Please add there things you find odd, missing, wrong, confusing or whatever about the OCM spec proposal. We will have a dedicated meeting on everything mentioned in #15 to agree on how to improve these things going forward.

[In-Ko]

FYI: The new place of the OCM Spec is now: https://github.com/gardener/ocm-spec. Everything we have will be moved there very soon.

[nab-gha]

Working on a PRs to implement the use of Kubernetes custom resource definition to describe the component descriptor and provide an illustration of using consumer component descriptor to reference a provider component descriptor as discussed during our meeting yesterday.

[In-Ko]

Working on a PRs to implement the use of Kubernetes custom resource definition to describe the component descriptor and provide an illustration of using consumer component descriptor to reference a provider component descriptor as discussed during our meeting yesterday.

Created #35 specifically for the work on that CRD.

[In-Ko]

Additionally created open-component-model/ocm-spec#3, open-component-model/ocm-spec#4 and open-component-model/ocm-spec#5 and updated https://github.com/gardener/ocm-spec/blob/main/doc/proposal/leftovers.md accordingly.
This issue here (the one you are looking at) will act as an umbrella item / epic now.

[jensh007]

Created issue gardener-attic/component-spec#84

[jensh007]

Added discsssions at ocm-spec repo: https://github.com/gardener/ocm-spec/discussions

[jensh007]

Contract chapter added.

[jensh007]

added Git repo for getting-started guide: https://github.com/open-component-model/getting-started

[In-Ko]

Will close this now, we track individual tweaks / changes / improvements on the Spec in individual tasks.