Add submission-to-decision time metric to editorial stats

[Chrystinne]

Part of #2620

This PR adds a new time metric to the editorial stats page: Submission to decision time (median days).

[Chrystinne]

That's what's displayed with projects on my local database after adding the new column (Submission to decision time (median days)):

from project.models import ActiveProject, PublishedProject

all_projects = [PublishedProject.objects.filter(is_legacy=False), ActiveProject.objects.all()]

for project_set in all_projects:
    for project in project_set:
        for log in project.edit_log_history():
            if log.decision_datetime and project.submission_datetime:
                duration = log.decision_datetime - project.submission_datetime
                print(f"{project} | decision={log.decision} | submission={project.submission_datetime.date()} | decision_date={log.decision_datetime.date()} | days={duration.days}")

Demo eICU Collaborative Research Database v2.0.0 | decision=1 | submission=2018-11-04 | decision_date=2018-11-14 | days=10
Demo eICU Collaborative Research Database v2.0.0 | decision=2 | submission=2018-11-04 | decision_date=2018-11-14 | days=10
Demo for visualizing waveforms v1.0.0 | decision=2 | submission=2020-12-23 | decision_date=2020-12-23 | days=0
Demo software for parsing clinical notes v1.0 | decision=2 | submission=2020-04-10 | decision_date=2020-04-10 | days=0
Demo eICU Collaborative Research Database | decision=2 | submission=2026-05-11 | decision_date=2026-05-11 | days=0
Demo software for parsing clinical notes | decision=0 | submission=2020-04-10 | decision_date=2026-05-13 | days=2223

2019 was a bit weird, so I found out that it was a demo project created directly as published, bypassing the normal editorial workflow:

from project.models import PublishedProject

p = PublishedProject.objects.filter(is_legacy=False, publish_datetime__year=2019).first()
print(p)
print("submission_datetime:", p.submission_datetime)
print("editor_assignment_datetime:", p.editor_assignment_datetime)
print("publish_datetime:", p.publish_datetime)
for log in p.edit_log_history():
    print("log decision:", log.decision, "| decision_datetime:", log.decision_datetime)

Demo 2018 BHI and BSN Data Challenge v1.0
submission_datetime: None
editor_assignment_datetime: None
publish_datetime: 2019-04-17 07:53:10.022000+00:00
log decision: 2 | decision_datetime: 2019-03-17 07:52:34.096000+00:00

[tompollard]

Is it possible to move some of the work into the query (following a similar approach to the stats above)?