Additional validation and escaping for file names.

This adds additional front and backend validations for task order file
names. We are now restricting file names to a whitelist regex of
[A-Za-z0-9\-_ \.] for simplicity.

Note:
On the frontend, the filename string must have at least one character.
This is not true in the backend validation; because of the way the
entire task order form is validated, requiring input would break the
business logic currently implemented.

translations.yaml

@@ -292,6 +292,7 @@ forms:
   task_order:
     upload_error: There was an error uploading your file. Please try again. If you encounter repeated problems uploading this file, please contact CCPO.
     size_error: The file you have selected is too large. Please choose a file no larger than 64MB.
+    filename_error: File names can only contain the characters A-Z, 0-9, space, hyphen, underscore, and period.
     defense_component_label: Select DoD component(s) funding your Portfolio
     file_format_not_allowed: Only PDF or PNG files can be uploaded.
     number_description: Task order number (13 digits)