Updates for new OAuth URL needed in multiple resources

[dstaudt]

As the PSIRT API is transitioning to a new OAuth URL:

OLD -https://cloudsso.cisco.com/as/token.oauth2
NEW - https://id.cisco.com/oauth2/default/v1/token

The URL needs to be updated in multiple areas through this repo, e.g. the OAS doc (readme comments), code examples, etc.

This search seems to capture all of them: https://github.com/search?q=repo%3ACiscoPSIRT%2FopenVulnAPI%20token.oauth2&type=code

[dstaudt]

The API base URL is also modified with this migration and will need to be modified throughout:

OLD: api.cisco.com
NEW: apix.cisco.com