Include git commit ID in configuration summary

[program--]

This PR adds the repo's git commit ID to the CMake configuration summary output. This will also include it when calling ngen --info.

Example:

NGen version: 0.1.0
-- Build configuration summary:
--   Generator: Ninja
--   Build type: Debug
--   System: Linux
--   C Compiler: /usr/bin/clang
--   C Flags: -Wpessimizing-move
--   CXX Compiler: /usr/bin/clang++
--   CXX Flags: -Wpessimizing-move -pedantic-errors
--   Git Commit ID: 2ffedf8ecb3d6311be65d8c7c8f99c2fecf7ee07
--   Flags:
...

Additions

• Adds NGEN_GIT_COMMIT CMake variable.

Checklist

• [X] PR has an informative and human-readable title
• [X] Changes are limited to a single goal (no scope creep)
• [X] Code can be automatically merged (no conflicts)
• [X] Code follows project standards (link if applicable)
• [X] Passes all existing automated tests
• [X] Any change in functionality is tested
• [X] New functions are documented (with a description, list of inputs, and expected output)
• [X] Placeholder code is flagged / future todos are captured in comments
• [X] Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• [X] Reviewers requested with the Reviewers tool :arrow_right:

[PhilMiller]

I see the print in configuration. How does it end up in ngen --info? Given that you show runtime output, with strings that don't exist in my repo, I'm guessing some code didn't get committed

[program--]

I see the print in configuration. How does it end up in ngen --info? Given that you show runtime output, with strings that don't exist in my repo, I'm guessing some code didn't get committed

The ngen_multiline_message and ngen_dependent_multiline_message CMake functions store their string arguments into a separate CMake variable NGEN_CONF_SUMMARY as a side effect. When NGenConfig.h is configured, that variable is outputted as a string here: https://github.com/NOAA-OWP/ngen/blob/2ffedf8ecb3d6311be65d8c7c8f99c2fecf7ee07/include/NGenConfig.h.in#L46

So for every ngen build, the exact build summary is embedded into it via that header

[PhilMiller]

Ah, that was a depth of cleverness that I hadn't realized. Excellent.