Suggest a PE number when PE number is not found

Using the defined format of a PE number
(https://www.militaryperiscope.com/terms/t0000241.html), we can suggest
a corrected format of the PE number if the user omitted the leading
zeros for either the DoD program or category.

tests/forms/test_financial.py

@@ -0,0 +1,14 @@
+import pytest
+
+from atst.forms.financial import suggest_pe_id
+
+
+@pytest.mark.parametrize("input,expected", [
+    ('0603502N', None),
+    ('0603502NZ', None),
+    ('603502N', '0603502N'),
+    ('063502N', '0603502N'),
+    ('63502N', '0603502N'),
+])
+def test_suggest_pe_id(input, expected):
+    assert suggest_pe_id(input) == expected