Improvement suggestions for multi-objective optimization tutorial

**Description**
Multi-objective optimization tutorial currently lacks several relevant information for being useful or fully understandable

**Proposal**
Below is a list of suggested improvements:
- [ ] Include link / path to where in the repository to find the configuration file to perform this multi-objective experiment
- [x] If the idea is to avoid repetition with respect to single objective well rate optimization experiment, include link to that tutorial doc to increase coherence across tutorials. If not, state explicitly somewhere that this is optimization of time-varying water injection rate targets
- [x] Add snippet from configuration file to show how to define multiple objectives in `objective_functions` section
- [x] Clearly indicate in the text what are the weights assumed for NPV and FWPT
- [x] Correct formula `f(x) = w_1 * npv(x) - w_2 * fwpt(x)`: it should be `f(x) = w_1 * npv(x) - w_2 * fwpt(x)` and stated that `fwpt` objective is to be minimized (therefore, multiplier -1 in `fm_extract_summary_data`)
- [x] Add snippet from configuration file to show usage of `fm_npv` and `fm_extract_summary_data` to generate objective function files
- [x] Improve objective function plots to display evolution of npv and fwpt objectives over iterations (instead of total combined objective only)
- [x] Unclear why there are two sets of results / plots at the end. Is there one multi-objective optimization experiment or two? The text only describes one experiment