Check compatibility with create_rft_ertobs handling of missing data

[berland]

The documentation

https://github.com/equinor/fmu-tools/blob/cc3581b44a4c0b9e8ff911f691cf8857f076d36a/docs/create_rft_ertobs.rst?plain=1#L35-L36

indicates that a value of -1 carries a special meaning. Verify this with Ert and make sure it is tested.

This behaviour seemingly leads to validation error in Ert currently, stating that the "Observation uncertainty must be strictly > 0".

[berland]

Ert changed behaviour two years ago on this in: https://github.com/equinor/ert/commit/5c68505a92d4aa309f5403c2733cefd6a5c68824

[berland]

https://github.com/equinor/fmu-tools/blob/main/src/fmu/tools/rms/create_rft_ertobs.py#L431-L432 sets the values -1 and 0

[berland]

This error has been shown to users 40 times the last 12 months.

[oyvindeide]

Setting as blocked, not sure the ert behavior warrants a change, somewhat related to: https://github.com/equinor/ert/issues/7967

[eivindjahren]

Seeing as this is being replaced, perhaps a temporary solution would be sufficient? We have been asked for the possibility of disabling observations except for plots so maybe solve that in conjunction?