[WIP] Conversion to any format supported by PowSyBl

[geofjamg]

• Do you want to request a feature or report a bug?
  Feature

• What is the current behavior?
  We can convert a case to xiidm using REST query

/cases/{caseName}?xiidm=true

• What is the expected behavior?
  We could improve the conversion capability of this service by allowing any conversion supported by powsybl core.

/cases/{caseName}?format=CGMES

In that case we also could provide an API to get supported formats.

/formats

=>

[
    "CGMES", 
    "UCTE", 
    "XIIDM"
]

• What is the motivation / use case for changing the behavior?

• Please tell us about your environment:

  • PowSyBl Version: ...
  • OS Version: ...

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

(if a question doesn't apply, you can delete it)