[backend] Add last seen when asset is registered through agent

[RomuDeuxfois]

Proposed changes

• Add last seen property when when asset is registered through agent

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 27.12%. Comparing base (0ab5ff1) to head (caaf336).

Files	Patch %	Lines
...va/io/openbas/rest/asset/endpoint/EndpointApi.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1120      +/-   ##
============================================
+ Coverage     26.82%   27.12%   +0.29%     
- Complexity     1057     1061       +4     
============================================
  Files           469      469              
  Lines         11105    11102       -3     
  Branches        562      562              
============================================
+ Hits           2979     3011      +32     
+ Misses         8041     8006      -35     
  Partials         85       85              

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