Custom filename for content-disposition

[jrchudy]

This PR adds support for an new annotation property on the asset annotation, stored_filename_pattern. This property will allow for data modelers to customize the content-disposition value that is stored in hatrac for the file and the value stored in the filename_column (if defined on the annotation). This pattern uses the same template variables as url_pattern with a new one added called filename_stem, the name of the file without the extension.

More details in the comment on issue 1949 in chaise.

[RFSH]

I think you should also update line 449 and 452 (where you recently changed so we would update the filename of already uploaded files) to use .storedFilename instead of .file.name.

Apart from that everything looks good to me and test cases passed locally.