Add Support For Remote TensorBoard Logs Via URL

[jmew]

Add an additional option when launching tensorboard to let users point tensorboard log-dir to a remote URL

1. use current working directory
2. Select another folder
3. Enter remote url (subheading: Enter a url pointing to a remote directory containing your TensorBoard log files)

When the new option is selected, show a VS Code input box for users to enter a url to their TensorBoard log file. If the file cannot be accessed, we should not need to do anything special as TensorBoard will handle that scenario.