Add optional remediation field to changeset

[drdavella]

Add optional metadata fields that can be populated by Codemodder when remediating findings from external tools.

This is currently unused by upstream tools but it may be useful to capture this metadata and could be useful going forward.

[nahsra]

• It seems like this information is duplicative to the codemod namespace. For instance, codeql:java/whatever implies the some of the information here. Do we care?
• How do we report the other stuff (the findings that were not fixed)? Should that be a subset at the root of a codemod's section of the CodeTF? E.g.:

"codemod" : "codeql:java/whatever",
"summary: "Description of rule/fix..",
"findings" : [
   { 
     "resultId" : "zxc-1",
     "outcome" : "FAILED_LOCATION_NOT_FOUND",
     "resultFile" : "my-codeql-sarif.sarif"
   },
   { 
     "resultId" : "zxc-2",
     "outcome" : "FAILED_SOURCE_NOT_FIXABLE",
     "resultFile" : "my-codeql-sarif.sarif"
   },
]

• I would record that resultId is a String and will contain vendor-specific ID values with an unpredictable character set.

[nahsra]

Will revisit as part of #17 .