[DOCS] OAuth authentication added to SN ITSM, SecOps, and ITOM connectors

[nastasha-solomon]

Dev issue: elastic/kibana#131260
Dev PR: elastic/kibana#131248

Support for OAuth authentication has been added to ServiceNow connectors in 8.3.

[nastasha-solomon]

Need the associated PR and issue as well as definitions for the new fields.

[nastasha-solomon]

Fixed in elastic/kibana#131344. @lcawl is further refining this content in elastic/kibana#133347.

cc: @cnasikas

[nastasha-solomon]

Need to mention the Use OAuth authentication setting in the Configure external connections topic. Will likely need to link users off to the connectors table here to point them towards docs describing requirements for using OAuth to authentication a connection between Elastic and SN.