Refactor experiment related stuff

[elikatsis]

• Choose from current experiments or create a new one

• If experiment is not set in notebook's metadata, choose first experiment by default

• Define IExperiment: {id, name}

• Define ISelectOption: {label, value} and use it wherever possible

• Introduce the field state.metadata.experiment: IExperiment

• Keep state.metadata.experiment_name: string, for backwards compatibility. Prefer state.metadata.experiment

• Add state.experiments: IExperiment[]

• Add state.gettingExperiments boolean to show Loading message

• Fix experiment name regex

This requires Kale RPC kfp.list_experiments.

Signed-off-by: Ilias Katsakioris elikatsis@arrikto.com