RTR: x-okapi-token, step 1; Implement AT and RT support.

[kaladay]

The AT and possibly the RT should be added.

The focus here is to add the models and other structures.
Switching over to this model is out of scope for this issue.

A new model should be created to represent these tokens, similar to how Tenant and Credentials are designed and used (focusing more on Credentials than Tenant).

This should be usable by functions like the okapiLogin() and headers().

These structures should handle the authentication process as appropriate.

see:

CatalogService/service/src/main/java/edu/tamu/catalog/properties/FolioProperties.java

Line 19 in edae26d

private String tenant;

see:

CatalogService/service/src/main/java/edu/tamu/catalog/properties/FolioProperties.java

Line 21 in edae26d

private Credentials credentials;