Add dedicated CI job for deprecation warnings

Part of #1847 (closed)

This is some backstage work for prepping for #1847 (closed). We need a way to track deprecated code usage so that we know when we have fully replaced known old/bad code.

Added:

• A dedicated CI job for tracking static analysis warnings. A warning is something we care about, but we don't want it to fail the pipeline. The only warning added is Staticcheck SA1019 for tracking deprecated code usage. (FYI, you can deprecate code with a dedicated comment paragraph that starts with Deprecated: , see this Go blog article for some details).

Changed:

• The verify stage will not error on deprecations since that is now handled by verfiy-warnings.
• Insecure Git command functions are marked as deprecated to get the needed changes on our radar for completing #1847 (closed).
• Makefile template string is moved to dedicated file to make it easier to find and edit (some of the Makefile syntax highlighting works now!).