Fix(commands/prune.rs): Add More detail in MissingWorkspace error (#7956)
### Description
Related to https://github.com/vercel/turbo/pull/7948, in running the
`turbo prune` when specifying a package name, it is assumed that the
package name is the name of the **folder** in `apps/web` or
`packages/eslint-config`. The real case is that the package name is the
name found in the `package.json` file in the `apps/*` directory.

This pull requests adds more detail and clarity towards the uncertainty
of defining what the package means.
**Files Edited**
Line 46 of
https://github.com/vercel/turbo/blob/main/crates/turborepo-lib/src/commands/prune.rs
```rs
#[error("invalid scope: package {0} not found")]
MissingWorkspace(PackageName),
```
to
```rs
#[error("invalid scope: package with name {0} in package.json not found")]
MissingWorkspace(PackageName),
```