Improve how users configures stratigraphy

[tnatt]

This is a larger issue which tries to link several issues into one.
Currently the current format of the stratigraphy block in the global config has several limitations

• stratigraphic_alias not added to metadata #852
• top/base name not converted to stratigraphic name #855
• name input is not checked against alias list #853
• top/base information often lacking for zones #854

The format should be improved so that (at minimum)

• there exists a clear relationship between zones and horizons
• the format is suitable for including this block into the case metadata e.g. under fmu.model.stratigraphy as it is important information in various visualization contexts.

thoughts

• improve user friendliness and allow for easy updates by creating a simplified export function of stratigraphy from the model from inside RMS e.g. "export_stratigraphy".
• keep the stratigraphy mapping to official SMDA names as separate dictionary
• could the .fmu be utilized in this new way?
• how to handle multiple stratigraphic columns and also grid zone names and the relationship between the intervals?
  

Other important issues related to mapping masterdata to fmu data, that might influence the thought process

• Support stratigraphic mapping of intervals covering multiple stratigraphic intervals #868
• ENH: Consider (!) dedicated link to stratigraphic column #851
• EPIC: Sustainable handling of master/reference data inside FMU #850
• Add the data name used in FMU explicitly to produced metadata #401