CA: stop mutating the result of .TemplateNodeInfo() in SanitizedTemplateNodeInfoFromNodeGroup

SanitizedTemplateNodeInfoFromNodeGroup() calls .TemplateNodeInfo(),
adds deprecated labels to the result, then sanitizes it - which includes
deep-copying.

This commit moves adding the deprecated labels after the sanitization
process, directly to the deep-copied result.

If .TemplateNodeInfo() caches its result internally, and is called
from a CloudProvider-specific goroutine at the same time as
SanitizedTemplateNodeInfoFromNodeGroup(), CA panics because of a
concurrent map read/write. This change removes the race condition.