debugger: some improvements in configuration handling

[cmaglie]

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• Tests for the changes have been added (for bug fixes / features)
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• configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

Added some small fix in how the debugger configuration is handled:

1. Allows non-sequential directives in properties, in particular for debug.server.openocd.scripts.N.
2. The debug.server.openocd.script directive is ignored if is together with the debug.server.openocd.scripts.N.

What is the current behavior?

1. The debug.server.openocd.scripts.N sequence was truncated at the first non-consecutive item.
2. Both script and scripts were concatenated in the resulting config.

What is the new behavior?

1. The debug.server.openocd.scripts.N sequence is not truncated even if the items are non-consecutive.
2. scipt and scripts are mutually-exclusive in the config with priority given to scripts.

Does this PR introduce a breaking change, and is titled accordingly?

Other information

[umbynos]

left some comments, Thanks cris

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (748fcf6) 62.92% compared to head (ce64d47) 62.92%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2364   +/-   ##
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  Coverage   62.92%   62.92%           
=======================================
  Files         203      203           
  Lines       19243    19243           
=======================================
  Hits        12108    12108           
  Misses       6075     6075           
  Partials     1060     1060           

Flag	Coverage Δ
unit	62.92% <100.00%> (ø)

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Files	Coverage Δ
commands/debug/debug_info.go	66.86% <100.00%> (ø)

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