feature/featuretags: make CLI connection error diagnostics modular

Updates #12614

Change-Id: I09b8944166ee00910b402bcd5725cd7969e2c82c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f