`--prepare-proposal-outputs` and `--prepare-localization-outputs` are not accepted by `actev exec`

The actev exec command is what we generally use to invoke the CLI. However, this command takes neither the --prepare-proposal-outputs nor the --prepare-localization-outputs arguments accepted by the actev experiment-init command. Therefore, if we want to test a CLI implementation using these arguments, we need to run a sequence of CLI commands which is inconvenient and makes running our deliverable system unnecessarily complicated.

I believe implementing these additional arguments for actev exec should be straightforward. If I understand the CLI code correctly, this change should be a matter of:

1. adding the arguments to the parser at bin/commands/actev_exec.py
2. forwarding the arguments to experiment_init in bin/private_src/implementation/exec/exec.py
3. and updating the argument list at doc/cli_commands/actev_exec.md.