agent: upgrade to caracal v0.15.2 to fix mangled lines on stdout

[maxmouchet]

See dioptra-io/caracal#61.

@SaiedKazemi the next steps would be:

1. Merge this PR
2. Merge main into production and wait for the new images to be built
3. Wait for watchtower to upgrade the containers, or iris down && iris pull && iris up -d
4. Upgrade GCP infrastructure: terraform destroy && terraform apply
5. Cancel the running measurements and trigger a new scheduler run

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (79caa55) 93.86% compared to head (8da7596) 93.86%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #171   +/-   ##
=======================================
  Coverage   93.86%   93.86%           
=======================================
  Files          54       54           
  Lines        2168     2168           
=======================================
  Hits         2035     2035           
  Misses        133      133           

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