Provide support for a corporate compliance warning when authenticating

[miclip]

Provide a means to configure a corporate legal notice when a user authenticates using pinniped-cli. Common for organisations to require a legal noticed be displayed when accessing corporate systems. Would mostly apply to LDAP/AD as OIDC should redirect to a service that can display the notice.

User executes kubectl cmd, pinniped challenges for credentials and displays a configured message, example below.

This system is company property and is provided for [company]-authorized
use only, including occasional personal use, as set forth in applicable
written policies. Unauthorized use is prohibited and may be subject to
discipline, civil suit and criminal prosecution. As [company] has a legitimate
interest in the security of this company resource as well as its efficient
and lawful use, any communications or data transiting or stored on this
system may be monitored, intercepted, recorded, and searched at any time
for any lawful purpose, and may be used or disclosed for any lawful purpose.
By using this system you understand and consent as follows: to comply with
all other applicable written policies, procedures and guidelines for system
use and protection of company information or information that the company
has an obligation to protect, including but not limited to Proprietary
Information, Personal Information/Personally Identifiable Information,
Controlled Unclassified Information, and Export Controlled Information.