rename objects in `reproduction_number_serological_data.qmd` to differentiate the dataset of observed and estimated values.

requested changes added. format now match required format output. The entry `reproduction_number_serological_data.qmd` may require some object renaming in `data_summary` and `summary_data` to clearly differentiate between the observed and estimated values. But we can do this in a separate PR too.

_Originally posted by @avallecam in https://github.com/epiverse-trace/howto/pull/57#pullrequestreview-2346303138_

Open reproduction_number_serological_data.qmd and inspect the data_summary and summary_data objects, using the referenced pull request context as needed. Rename the objects or their relevant fields so observed and estimated values are clearly differentiated, then confirm the guide still produces the required format output.

Written by the indexing model from the issue text.