introduce mapocirepoattr to control OCI artifact upload

[mandelsoft]

What this PR does / why we need it:

When transferring an OCM component version into an OCI registry based OCM repository, by default, an OCI artifact
uploader is used to publish OCI artifacts stored as local blobs to the same OCI registry. Here, the repository hint is
used to calculate an OCI repository name for the uploaded OCI artifact based on the repository path of the OCM repository.

This results in in potentially very long names, Artifactory has problems with this, therefore we need a possibility to abbreviate
those generated names.

This PR provide a new context attribute to control the upload behaviour. It is possible now to abbreviate the repository hing
by a hashed version all but the last name segaments. It is possible to chose between three modes:

• simple hash (might still be too long)
• short hash (like for Git, with the first 8 characters of the hash)
• prefix mapping. use to map hint prefixes to possibly shorter names.

This attribute can be set with the -X options, or the attribute configuration feature for .ocmconfig.
The attribute name/short name is

	ATTR_KEY   = "github.com/mandelsoft/ocm/mapocirepo"
	ATTR_SHORT = "mapocirepo"

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release Notes:

[morri-son]

tested successfully.