[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 https://github.com/hugsy/gef/pull/1120 before merging.

[github-actions[bot]]

🤖 Coverage update for fd5b5e1e58a1dfcccf4b8df9ab37fb4c2a460fbb 🟢

	Old	New
Commit	c450a2d5fdd6f3e58fcadf8fe97365c8a36c6172	fd5b5e1e58a1dfcccf4b8df9ab37fb4c2a460fbb
Score	71.6798%	71.6798% (0)

[github-actions[bot]]

🤖 Coverage update for fd5b5e1e58a1dfcccf4b8df9ab37fb4c2a460fbb 🔴

	Old	New
Commit	c450a2d5fdd6f3e58fcadf8fe97365c8a36c6172	fd5b5e1e58a1dfcccf4b8df9ab37fb4c2a460fbb
Score	71.6798%	71.6649% (-0.0149)

[github-actions[bot]]

🤖 Coverage update for 84b2afdb9270c05b271656f6a0b772c37ec23c6c 🟢

	Old	New
Commit	c450a2d5fdd6f3e58fcadf8fe97365c8a36c6172	84b2afdb9270c05b271656f6a0b772c37ec23c6c
Score	71.6798%	71.6798% (0)

[github-actions[bot]]

🤖 Coverage update for 84b2afdb9270c05b271656f6a0b772c37ec23c6c 🔴

	Old	New
Commit	c450a2d5fdd6f3e58fcadf8fe97365c8a36c6172	84b2afdb9270c05b271656f6a0b772c37ec23c6c
Score	71.6798%	71.6649% (-0.0149)