FEATURE: Simplify the validity joins with dplyr::join_by.

[RasmusSkytte]

Describe the feature
When filtering the validity periods in diseasystore, we often have to copy the dates to the remote connection and then filter using an inner_join with an sql_on argument.

This syntax is more confusing than the new dplyr::join_by() syntax for the corresponding joins.

An example of the bad syntax can be seen in the simulist_age FeatureHandler in #162 which is confusing for the user.

SCDB has a pull request open for allowing dplyr::join_by() in its joins (ssi-dk/SCDB#156)
Once released, we should implement in diseasystore to simplify the code

What use will this feature have?
Improved readability. Easier implementation of new diseasystores.

Who should add the feature?
N/A

Additional context
N/A