[DOWNSTREAM] rename `veneer` to `template` for all code, docs references

This is the downstreaming issue for the upstream operator-registry changes. Upstream olm-docs repo will be downstreamed as part of later docs updates.
https://docs.google.com/document/d/139yXeOqAJbV1ndC7Q4NbaOtzbSdNpcuJan0iemORd3g/

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Veneer is viewed as a confusing and counter-intuitive term.  PM floated `catalog template` (`template` for short) as a replacement and it's resonated sufficiently with folks that we want to update references/commands to use the new term. 

A/C:

• updates to all upstream docs (olm.operatorframework.io)
• updates to hackmd references (hierarchy head at https://hackmd.io/O-DelGCnRbSmioFYnuBqkA)
• updates to operator-registry commands (strongly prefer to also make changes to code paths, module names, etc. to make the change consistently)
• updates to the generated demo for semver (or deletion.... really, the thing here is to be consistent)
• Docs audit (collaboration with docs rhn-support-mipeter and rhn-support-adellape )
• creation of a new downstreaming story to populate the changes to master, 4.12 so that early adopters aren't ambushed by what is merely a name change.