dedupe the activity feed

[owocki]

Description

This change makes sure there are never ever dupes in the activity feed.

An example of dupes from gitcoin.co/activity:

Refers/Fixes

Self

Testing

run this script:

In [1]: from dashboard.models import Activity

In [2]: activity = Activity.objects.last()

In [3]: activity.pk = None

In [4]: activity.pk = None; activity.save()

In [5]: activity.pk = None; activity.save()

In [6]: activity.pk = None; activity.save()

In [7]: activity.pk = None; activity.save()

In [8]: activity.pk = None; activity.save()

In [9]: activity.pk = None; activity.save()

In [10]: activity.pk = None; activity.save()

and inspect http://localhost:8000/_administrationdashboard/activity/
http://localhost:8000/activity
to make sure there are no dupes

[codecov]

Codecov Report

Merging #4947 into master will increase coverage by 0.05%.
The diff coverage is 93.75%.

@@            Coverage Diff            @@
##           master   #4947      +/-   ##
=========================================
+ Coverage   30.84%   30.9%   +0.05%     
=========================================
  Files         217     217              
  Lines       17397   17413      +16     
  Branches     2376    2378       +2     
=========================================
+ Hits         5366    5381      +15     
+ Misses      11814   11813       -1     
- Partials      217     219       +2

Impacted Files	Coverage Δ
app/dashboard/models.py	56.8% <93.75%> (+0.34%)	⬆️
app/dashboard/views.py	14.29% <0%> (ø)	⬆️

---

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[codecov]

Codecov Report

Merging #4947 into master will increase coverage by 0.05%.
The diff coverage is 93.75%.

@@            Coverage Diff             @@
##           master    #4947      +/-   ##
==========================================
+ Coverage   30.63%   30.69%   +0.05%     
==========================================
  Files         216      216              
  Lines       17496    17512      +16     
  Branches     2389     2391       +2     
==========================================
+ Hits         5360     5375      +15     
+ Misses      11920    11919       -1     
- Partials      216      218       +2

Impacted Files	Coverage Δ
app/dashboard/models.py	56.78% <93.75%> (+0.34%)	⬆️
app/dashboard/views.py	14.19% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5ee10bd...2f9d008. Read the comment docs.