Fix capitalization of "container registry"

What does this MR do?

As a first followup to the linked MR, this starts fixing the capitalization of "container registry" to always be lowercase (unless at the start of a sentence, header, etc).

This is not an exhaustive update of all the terminology, I did a find-and-replace on phases that I could be confident could be updated, for example:

• a/the Container Registry => a/the container registry (starts with a or the, so it's not starting a sentence or anything)
• - [Container Registry => - [Container registry (lowercase r when starting a bullet point)
• # Container Registry => # Container registry (Like above, for headers)

Related issues

• Related to !136400 (merged)

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