feat(cli): Add --target-dir option

[aakoshh]

Description

Problem*

Resolves #7349

Summary*

Adds a --target-dir option to the nargo CLI which can be used to override the default target directory location, which is based on the --program-dir.

Additional Context

Initially I added this as a new parameter to the TOML functions we use to resolve the Workspace, so we don't forget to set it, but as it turned out the majority of places where we parse the manifest don't actually need the target directory, because they don't read artefacts produced by other commands. The only ones that seem to care are the ones that were refactored to take a Workspace already.

Here's a demonstration:

$ cd test_programs/execution_success/workspace/crates/a
$ cargo run -q -p nargo_cli -- execute --package b
[b] Circuit witness successfully solved
[b] Witness saved to /Users/aakoshh/Work/aztec/noir/test_programs/execution_success/workspace/target/b.gz
$ cargo run -q -p nargo_cli -- --target-dir ./my-target execute --package b
[b] Circuit witness successfully solved
[b] Witness saved to /Users/aakoshh/Work/aztec/noir/test_programs/execution_success/workspace/crates/a/my-target/b.gz

Note that the --target-dir comes after --, otherwise it's interpreted as a parameter to cargo itself, in which case it would use my-target to compile nargo itself.

The docs only mention --program-dir in relation to the export command, and --program-dir itself is a hidden option, so I kept --target-dir hidden as well.

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[michaeljklein]

LGTM