Add sodiff to 2.0 toolkit

[MateuszMalisz]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• [X] The toolchain has been rebuilt successfully (or no changes were made to it)
• [X] The toolchain/worker package manifests are up-to-date
• [X] Any updated packages successfully build (or no packages were changed)
• [X] Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• [X] Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• [X] All package sources are available
• [X] cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/tools/cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• [X] LICENSE-MAP files are up-to-date (./SPECS/LICENSES-AND-NOTICES/data/licenses.json, ./SPECS/LICENSES-AND-NOTICES/LICENSES-MAP.md, ./SPECS/LICENSES-AND-NOTICES/LICENSE-EXCEPTIONS.PHOTON)
• [X] All source files have up-to-date hashes in the *.signatures.json files
• [X] sudo make go-tidy-all and sudo make go-test-coverage pass
• [X] Documentation has been updated to match any changes to the build system
• [X] Ready to merge

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Summary

What does the PR accomplish, why was it needed? Sodiff was not present in 2.0 toolkit. This PR adds sodiff capability to 2.0 Mariner. This change includes the SODIFF_OPTIONAL_SOURCES changes.

Change Log

• Add sodiff to 2.0.
• Add SODIFF_OPTIONAL_SOURCES variable.
• Add documentation for the new variable.

Does this affect the toolchain?

NO

Test Methodology

• Local build