RFE: opm alpha render-veneer semver should recognize multiple schema in an input veneer

[grokspawn]

When multiple schema instances are listed in the same doc via the new-doc delimiter (---) the render should process each schema independently, in sequence, for e.g.:

Schema: olm.semver
GenerateMajorChannels: true
GenerateMinorChannels: false
Stable:
  Bundles:
  - Image: repository-uri/example-operator:v0.8.9
  - Image: repository-uri/example-operator:v0.9.0
---
Schema: olm.semver
GenerateMajorChannels: true
GenerateMinorChannels: false
Stable:
  Bundles:
  - Image: repository-uri/another-example-operator:v0.8.9
  - Image: repository-uri/another-example-operator:v0.9.0

Errors would be fatal to processing that independent schema..