TLS was not being verified in a number of places:
- connections to grafana.com
- connections to OAuth providers when TLS client authentication was
enabled
- connections to self-hosted Grafana installations when using the CLI
tool
TLS should always be verified unless the user explicitly enables an
option to skip verification.
Removes some instances where `InsecureSkipVerify` is explicitly set to
`false`, the default, to help avoid confusion and make it more difficult
to regress on this fix by accident.
Adds a `--insecure` flag to `grafana-cli` to skip TLS verification.
Adds a `tls_skip_verify_insecure` setting for OAuth.
Adds a `app_tls_skip_verify_insecure` setting under a new `[plugins]`
section.
I'm not super happy with the way the global setting is used by
`pkg/api/app_routes.go` but that seems to be the existing pattern used.