[CleanRepo] Add a command to compare / list latest commit, size and ms.date metadata

[BillWagner]

We think there are situations where an article gets a major update, but the ms.date metadata isn't updated in that commit. To find those, add a command to CleanRepo that traverses all the source files in the local copy of the repo and compares the dates of recent commits to the ms.date value.

To get the commit history, a query like this works:

query FileHistory {  repository(owner: "dotnet", name: "docs") 
{
    defaultBranchRef{
      target {
        ...on Commit{
            history(first:10,path: "docs/csharp/fundamentals/program-structure/top-level-statements.md"){
            nodes {
              committedDate
              changedFilesIfAvailable
               additions
              deletions
            }
          }
        }
      }
    }
  }
}

To find the ms.date value, the metadata block for each file needs to be read. Also, the docfx.json file needs to be partially processed to read any global metadata for ms.date and any file path based metadata for ms.date.

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Associated WorkItem - 360306

[BillWagner]

Fixed in #469