match restic exit codes

[judahrand]

restic has some well defined exit code which help when using it in scripts. These exit codes are defined in the documentation. It would be fantastic if rustic could maintain compatibility with these exit codes as it would make migration to rustic much easier. There are clearly some exit codes, for example code 11 which relates to locking which rustic would never use but the others are relevant.

[nardoor]

This is something I wouldn't mind doing at all.

For context, rustic_core error management was totally refactored recently.
Once it is stable we can probably start there.

[simonsan]

Current state of affairs:

✅ = implemented, ⚠️ = inconsistent, ❌ = not implemented, yet

Code	Description	status in rustic
0	Command was successful	✅
1	Command failed, see command help for more details	⚠️
2	Go runtime error	(not applicable)
3	backup command could not read some source data	❌
10	Repository does not exist (since restic 0.17.0)	❌
11	Failed to lock repository (since restic 0.17.0)	(not applicable)
12	Wrong password (since restic 0.17.1)	❌
130	Restic was interrupted using SIGINT or SIGSTOP	✅

[aawsome]

For exit codes > 128, se should follow the standard exit codes, see https://tldp.org/LDP/abs/html/exitcodes.html.
And this already works - interrupting rustic by SIGINT gives error code 130, SIGSTOP gives 147.