feat: Add custom_property events

[acouvreur]

custom_property and custom_property_values events are added.

Closes #3207

• I have run script/fmt.sh
• I have run script/test.sh
• I have run script/lint.sh
• I have run script/generate.sh because changes were detected

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.30%. Comparing base (2b8c7fa) to head (2904eba).
Report is 192 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3379      +/-   ##
==========================================
- Coverage   97.72%   92.30%   -5.42%     
==========================================
  Files         153      176      +23     
  Lines       13390    15031    +1641     
==========================================
+ Hits        13085    13874     +789     
- Misses        215     1064     +849     
- Partials       90       93       +3     

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[gmlewis]

Thank you, @acouvreur!
One minor tweak, please, then we should be ready for a second LGTM+Approval from any other contributor to this repo before merging.

[acouvreur]

Thank you, @acouvreur! One minor tweak, please, then we should be ready for a second LGTM+Approval from any other contributor to this repo before merging.

Done!

[gmlewis]

Thank you, @acouvreur !
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[stevehipwell]

LGTM

[gmlewis]

Thank you, @stevehipwell !
Merging.