Feature: Cache Tailscale credentials

[aaomidi]

When tailscale's systems are having an outage, this causes an immediete disruption to anyone using this action to get their CI on their tailnet.

This action can cache the credentials used in the past (possibly with a user defined cache key so we don't have workflows using each others credentials). If the credentials are still valid, then we would remove a strong dependency on the coordination server.

[aaomidi]

Alternatively, a built in healthcheck for the actions such as what I've described here may work too: #107 (comment)