[Feature]: Add extra_vars parameter to climo, as in ts

[forsyth2]

How will this affect the next version number?

Small improvement (increment PATCH version)

Is your feature request related to a problem?

In #533, we found that we had to set vars='' in order for landfrac to not cause issues when running climo for land variables.

Describe the solution you'd like

A more robust solution would be to set extra_vars -- however that option is only available for ts currently, not for climo. This option was introduced to ts in #120, #124.

Describe alternatives you've considered

No response

Additional context

No response