Fix minor issues in dynsec plugin

[SteveHamann]

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This PR includes minor improvements of the Dynamic Security Plugin. It improves validation of priority values, fixes issues in memory management and corrects the algorithm for generating random passwords on init. Where missing additional tests have been implemented to verify the correctness of the changes. This also includes a new directory for unit tests of the Dynamic Security Plugin.

[codecov]

Codecov Report

❌ Patch coverage is 72.22222% with 10 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
plugins/dynamic-security/clients.c	45.45%	6 Missing ⚠️
plugins/dynamic-security/roles.c	40.00%	3 Missing ⚠️
plugins/dynamic-security/config_init.c	85.71%	1 Missing ⚠️

Files with missing lines	Coverage Δ
plugins/dynamic-security/groups.c	85.06% <100.00%> (+1.27%)	⬆️
plugins/dynamic-security/rolelist.c	83.16% <100.00%> (+0.99%)	⬆️
plugins/dynamic-security/utils.c	100.00% <100.00%> (ø)
plugins/dynamic-security/config_init.c	72.86% <85.71%> (-0.11%)	⬇️
plugins/dynamic-security/roles.c	82.44% <40.00%> (+0.97%)	⬆️
plugins/dynamic-security/clients.c	81.95% <45.45%> (+0.57%)	⬆️

... and 2 files with indirect coverage changes

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