I renamed `tlsAuth` to `tlsClientAuth` to better describe the fact that
this variable is used to enable TLS client authentication (as opposed to
server authentication) in c04d95f35.
However, changing the name breaks backwards compatibility for existing
installations using this feature and Grafana does not have a
standardised way of migrating changes in the schema:
https://github.com/grafana/grafana/pull/9377#issuecomment-333063543
For reasons of expediency given the severity of the bug (not verifying
TLS), keep the old name.
In c04d95f35 I changed the default for datasource HTTP requests so that
TLS is always verified.
This commit adds a checkbox to allow an admin to explicitly skip TLS
verification, for testing purposes.