[backend] Domain observable checker is incorrect (#7620)

[SarahBocognano]

Proposed changes

• Change the regex to also accept dots on subdomain

Related issues

• Domain observable with underscore is incorrectly rejected #7620

[SouadHadjiat]

unit tests are failing on this PR, also could you add corresponding unit test for the usecase we are fixing ?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.95%. Comparing base (e17b1ed) to head (49d07c7).
Report is 23 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8768      +/-   ##
==========================================
+ Coverage   66.29%   66.95%   +0.65%     
==========================================
  Files         597      597              
  Lines       60958    60983      +25     
  Branches     6261     6701     +440     
==========================================
+ Hits        40414    40831     +417     
+ Misses      20544    20152     -392     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.