Implementation of port discovery through Pluggable discovery

[cmaglie]

Please check if the PR fulfills these requirements

• [X] The PR has no duplicates (please search among the Pull Requests before creating one)
• [X] Tests for the changes have been added (for bug fixes / features)

• What kind of change does this PR introduce? The port discovery is offloaded from the agent and it's made available through pluggable-discoveries (as done other Arduino software products like Arduino IDE or Arduino CLI)

• What is the current behavior? The port discovery subroutine was embedded in the Create Agent (leading to code duplication and double maintenance effort)

• What is the new behavior? The port discovery subroutine is off-loaded to pluggable discvoeries.

• Does this PR introduce a breaking change? No

• Other information: Supersedes #773