Observed summary data: Add parsing of ERT observed data file

[hhgs]

Parse ERT observed data file.
Consider using the ert-model as reference: Drogon example: ./ert/model/drogon_ahm.ert
DEFINE <OBS_FILE> ../input/observations/drogon_wbhp_rft_wct_gor_tracer_4d_plt.obs

From the .obs-file:
Import "SUMMARY_OBSERVATION"
Import "GENERAL_OBSERVATION" when referencing to ./rft/<well_name>.obs
Import "RFT_OBSERVATION" rft_obs { CSV=path/to/observation_file.csv;};

Reference documentation:
https://ert.readthedocs.io/en/latest/reference/configuration/observations.html#rft-observation