Document the auth-session CLI commands

[jseldess]

Jesse Seldess commented:

These commands were introduced in 19.2 but have not yet been documented.

PR: cockroachdb/cockroach#44110

From release notes:

Three new CLI commands, cockroach auth-session login, cockroach auth-session list, and cockroach auth-session logout, are now provided to facilitate the management of web sessions. The command auth-session login also produces a HTTP cookie which can be used by non-interactive HTTP-based database management tools. It also can generate such a cookie for the root user, who would not otherwise be able to do so using a web browser. [#44110][#44110] {% comment %}doc{% endcomment %}

SQL admins can now use the new command cockroach auth-session login to create authentication tokens with an arbitrary expiration date. Operators should be careful to monitor system.web_sessions and enforce policy-mandated expirations using either SQL queries or the new command cockroach auth-session logout. [#44110][#44110] {% comment %}doc{% endcomment %}

Jira Issue: DOC-424