import should not fail when snippet has already been imported

[polarathene]

Raising an issue from this community discussion.

The problem config used import several times where the same snippet was imported and caused a conflict error. However while the snippet name was the source of conflict, the contents of the snippet was identical (same import source too), thus it's not really a conflict.

This would also occur without import (which I understand is effectively equivalent to copy/paste), by declaring the same snippet twice in a single Caddyfile.

Solution proposed was for such an error to compare the two snippets via a content hash. If they're the exact same snippet then instead of an error, the subsequent imports could be ignored (or if the error happens at a later stage of validation, deduped).

Workaround suggested was to avoid the named snippet syntax and just use import on individual files without the snippet syntax wrapping it.