[BUG] REST API does not allow folder specification in filename

[jtsextonMITRE]

When uploading a plugin file, using a '/' character in the filename returns an error, making it so that folder specification cannot be used when uploading plugin files.

The following regex should be updated to fix this.

dioptra/src/dioptra/restapi/v1/plugins/schema.py

Line 35 in c289747

ALLOWED_PLUGIN_FILENAME_REGEX = re.compile(r"^([A-Za-z]|[A-Za-z_][A-Za-z0-9_]+)\.py$")