allow filtering timeentries by workpackage ids

[individual-it]

This allows the template to filter the timeentries by workpackages.
It is useful when limiting the export to a particular tmetric project (#22). If in that case we also want to use AllTimeEntriesFromOpenProject in the template, only the entries should be shown that were returned by the tmertric report

In the template all workpackages can be collected while looping through the report items e.g. by {{- $allWorkpackages = (append $allWorkpackages $reportItem.WorkpackageId | uniq) }}

and then to generate the list of time entries from Openproject that list of workpackages can be given to AllTimeEntriesFromOpenProject
e.g. {{- range $j,$timeEntry := AllTimeEntriesFromOpenProject $user $allWorkpackages }}