create a secret - doesn't trim content type

Found in: dev

Description: Running create secret tests with content type of "text/plain " (note the trailing space) fails with http 400. Same result if you specify the encoding with a trailing space (such as "text/plain; charset=utf-8 ")

Test Case: test_creating_secret_normalize_content_type_text_plain_trailing_space
also test_creating_secret_normalize_content_type_text_plain_space_charset_utf8_trailing_space

Reproduction Steps:

1) create a secret with a content type of 'text/plain ' or 'text/plain; charset=utf-8 '

   POST http://.../v1/{tenant_id}/secrets

Request:
<Secret object>
name = None
algorithm = None
payload_content_type = text/plain <-- there is a trailing space here
payload_content_encoding = None
content_types = None
expiration = None
bit_length = None
payload = testdata
mode = None

Actual Response:
http 400

Expected Response:
http 201 (successful creation)