Granule-url_description_uniqueness_check fixes 1 #324

[bhawana11]

This is a pull request for issue #324 url_description_uniqueness_check (Granule).

Expected outcome:
The PyQuARC error at the bottom of the results page with the following message
'ERROR: Running check for the rule: 'url_description_uniqueness_check' failed.. Details: sequence item 0: expected str instance, NoneType found' should not be seen.

Code Changes:
Added a override for 'url_description_uniqueness_check" in rules_override.json file.

To Reproduce:
Example concept ID: G2693552851-CDDIS (umm-g)

[lavanya3k]

Check for the granule G1811369774-CDDIS (umm-g)

[lavanya3k]

Description of the fix: The above code changes were reviewed and tested on umm-g and echo-g granules. The error url_description_uniqueness_check existed for the umm-c schema, and it was not resolved. Additionally, there was a similar error, online_access_description_uniqueness_check, for the echo-g schema.
The code changes are made in the rule_mapping.json and tested for quality control.

Output: You will NOT see the PyQuARC errors when it is run for Granules (umm-c and echo-g)
ERROR: Running check for the rule: 'url_description_uniqueness_check' failed
ERROR: Running check for the rule: 'online_access_description_uniqueness_check' failed.

Granules tested:
G1811369774-CDDIS --format umm-g
G1792338802-CDDIS --format umm-g
G2693552851-CDDIS --format umm-g
G2488091813-CDDIS --format echo-g
G1763305132-CDDIS --format echo-g

[lavanya3k]

@slesaad - Can you ignore the code changes from schema_validator.py due to conflicts from other local branches?