Improve series interface

Currently, the interface for recording series is missing some information required to create meaningful figures. At least, I would expect for each series:

- Name for the vertical axis (missing)
- Units for the vertical axis (missing)
- Name for the horizontal axis ([available](https://github.com/Climate-REF/climate-ref/blob/93e5e4adebad1fbdc55a1566c4fd83ddbe538b17/packages/climate-ref-core/src/climate_ref_core/metric_values/typing.py#L60-L65))
- Units for the horizontal axis (missing)
- A short piece of text describing the figure (missing)

Time units should include the [calendar](https://cfconventions.org/cf-conventions/cf-conventions.html#calendar).

For the ESMValTool series, I solved this by storing some of the information as attributes ([code](https://github.com/Climate-REF/climate-ref/blob/93e5e4adebad1fbdc55a1566c4fd83ddbe538b17/packages/climate-ref-esmvaltool/src/climate_ref_esmvaltool/diagnostics/base.py#L223-L257)), but it would be better to make these mandatory fields:
https://github.com/Climate-REF/climate-ref/blob/93e5e4adebad1fbdc55a1566c4fd83ddbe538b17/tests/test-data/regression/esmvaltool/global-mean-timeseries/cmip6_CMIP6.C4MIP%20CDRMIP.CSIRO.ACCESS-ESM1-5.esm-1pct-brch-1000PgC.r1i1p1f1.Amon.tas.gn.v20191206/series.json#L210-L221