Add `discouraged_for_mapping` flag for CWEs

[velac01]

Description

While doing research I noticed CWEs like CWE-20 are "Usage: Discouraged (this CWE ID should not be used to map to real-world vulnerabilities)"

Because of this, we see CVEs with a number of attack patterns like this because it's mapped to CWE-20.

Since the CWE is discouraged for use it should not be used in the mapping table.

Need to figure out a way to see what CWEs are listed with this status because it is not mentioned in the data feed download used to populate the database.

[velac01]

I asked Bard and this is what it said

Could be worth checking the CWE sites? then we could add a check in the DB to remove these from the mapping table.

[velac01]

The above is invalid, we might have to manually search.

[velac01]

• CWE-200 is discouraged for mapping!
• CWE-74 is discouraged for mapping!

[velac01]

Add a boolean to the cwe table to note that it isn't supposed to be mapped to vulns