[internal] Add a way to append values to optional arguments in parse_arguments decorator

[ValekoZ]

Add support for the append action for ArgumentParser in the parse_arguments decorator on optional arguments.

This makes us able to support this:

command --arg 1 --arg 2 --arg 3

And get [1, 2, 3] as the arg value.

This CL is required to make changes to #1120 before merging.

[github-actions]

🤖 Coverage update for fd5b5e1 🟢

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Commit	c450a2d	fd5b5e1
Score	71.6798%	71.6798% (0)

[github-actions]

🤖 Coverage update for fd5b5e1 🔴

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Commit	c450a2d	fd5b5e1
Score	71.6798%	71.6649% (-0.0149)

[hugsy]

Minor tiny fix
Thanks for the PR tho, I was certain we already had that

[github-actions]

🤖 Coverage update for 84b2afd 🟢

	Old	New
Commit	c450a2d	84b2afd
Score	71.6798%	71.6798% (0)

[github-actions]

🤖 Coverage update for 84b2afd 🔴

	Old	New
Commit	c450a2d	84b2afd
Score	71.6798%	71.6649% (-0.0149)