sanitize-commit: Validate Coverity-Id footers

Like for other footers, complain if

- the capitalization is wrong

- more than one CID is listed per line

- the CIDs are not numerical (catching Coverity-Id: CID-12345)

- the CIDs start with a leading zero (012 could be interpreted as
  octal, and there's no tradition to use leading zeros for CIDs,
  unlike, e.g. for QUIPs)

Change-Id: Ibb2fa705aad5a43b0e5d11895e019e2873cfdfe8
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>