Add support for external blob values in robotinterface

[PeterBowman]

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It is possible to externally (i.e. outside the XML robot configuration) override any parameters marked as extern-name with compound (lists) or simple (strings, integers...) values. This patch adds support for blobs, with unit testing (also covering external lists for completeness).

Use case: https://github.com/roboticslab-uc3m/yarp-devices/issues/271#issuecomment-1879676086.

[PeterBowman]

Windows builds are failing, I'm going to submit a fix soon.

[sonarqubecloud[bot]]

Quality Gate failed

Failed conditions

44.7% Coverage on New Code (required ≥ 80%)
26.5% Duplication on New Code (required ≤ 3%)

See analysis details on SonarCloud

[PeterBowman]

Windows builds are failing, I'm going to submit a fix soon.

Fixed, there's nothing a double pointer can't do :smirk:.