feat: don't remove user email from activity feed when user deleted

[jahzielv]

Checklist for submitter

If some of the following don't apply, delete the relevant line.

• Changes file added for user-visible changes in changes/ or orbit/changes/.
  See Changes files for more information.
• Input data is properly validated, SELECT * is avoided, SQL injection is prevented (using placeholders for values in statements)
• Added/updated tests
• Manual QA for all new/changed functionality

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (182ce61) 58.98% compared to head (e385f10) 58.99%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14975   +/-   ##
=======================================
  Coverage   58.98%   58.99%           
=======================================
  Files         956      957    +1     
  Lines       80692    80727   +35     
  Branches     2251     2251           
=======================================
+ Hits        47600    47627   +27     
- Misses      29396    29402    +6     
- Partials     3696     3698    +2     

Flag	Coverage Δ
backend	59.69% <78.94%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
server/datastore/mysql/activities.go	80.31% <100.00%> (+2.24%)	⬆️
server/fleet/activities.go	0.00% <ø> (ø)
.../tables/20231109115838_AddUserEmailToActivities.go	63.63% <63.63%> (ø)

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[getvictor]

Overall looks good. Please review my comments and make changes if needed.

[getvictor]

LGTM