Creating ensembes/experiments with unique names is not consistent

[oyvindeide]

In some places in the ert gui we have enforced that experiment names and ensembles must be unique, but that is not always enforced, as it is possible to make a new experiment in Experiment manager with a duplicate name. This is mostly not a problem, but will make it hard to tell the difference when plotting for example, or doing restart of es-mda.

• [x] https://github.com/equinor/ert/issues/7892
• [x] https://github.com/equinor/ert/issues/7893
• [x] https://github.com/equinor/ert/issues/7895
• [x] https://github.com/equinor/ert/issues/7913