Allow the user to specify {fqbn} parameter in the commandline

[umbynos]

Please check if the PR fulfills these requirements

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

• What kind of change does this PR introduce?

fix regression

• What is the current behavior?

After #878 the agent is no longer able to run the firmware uploader tool since it used an hack to expand FQBN and port:

{
  "board": "arduino:renesas_uno:unor4wifi",
  "port": "/dev/cu.usbmodemDC5475C5557C2",
  "commandline": "\"{runtime.tools.arduino-fwuploader.path}/arduino-fwuploader\" firmware flash {network.password} -v --retries 5",
  "signature": "...",
  "filename": "UpdateFirmware.bin",
  "extra": {
    "auth": {
      "password": "-a /dev/cu.usbmodemDC5475C5557C2 -b \"arduino:renesas_uno:unor4wifi\""
    }
  },
  "hex": ""
}

extra.auth.password was removed in #878 because it was linked to network upload.

• What is the new behavior?

{
  "board": "arduino:renesas_uno:unor4wifi",
  "port": "/dev/cu.usbmodemDC5475C5557C2",
  "commandline": "{runtime.tools.arduino-fwuploader.path}/arduino-fwuploader firmware flash -a {serial.port} -b {fqbn} -v --retries 5",
  "signature": "...",
  "filename": "UpdateFirmware.bin",
  "hex": ""
}

{fqbn} gets expanded with the content of board

• Does this PR introduce a breaking change?

Nop

• Other information:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 20.94%. Comparing base (16f322f) to head (6f12fb5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #905      +/-   ##
==========================================
+ Coverage   20.91%   20.94%   +0.02%     
==========================================
  Files          43       43              
  Lines        3160     3161       +1     
==========================================
+ Hits          661      662       +1     
  Misses       2403     2403              
  Partials       96       96              

Flag	Coverage Δ
unit	20.94% <100.00%> (+0.02%)	⬆️

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