Support specifying output directory path for detect-and-track-video

[sfmig]

Right now the --output-dir flag in the detect-and-track-video command allows the user to specify the name of the output directory, which is created under the directory the command is run from. By default, the directory name is tracking_output (in line with the evaluation_output). A suffix with the timestamp is added to the selected name.

However it would be convenient if additionally the users can select where this directory is created.