fix: Revert setting credentials providers by default in .cargo/config.toml with the :cargoSyncConfig task

[NiklasRosenstein]

Reverts the changes in #153 that set the [registry].global-credential-providers in .cargo/config.toml as the default, and instead adds a property that would still allow setting it.

The issue is that in our CI it seems that libsecret is not currently available

error: failed to get `xyz` as a dependency of package `abc v0.0.0 (/builds/abc/abc-rs/comments)`
Caused by:
  credential provider `cargo:libsecret` failed action `get`
Caused by:
  failed to load libsecret: try installing the `libsecret` or `libsecret-1-0` package with the system package manager
Caused by:
  libsecret-1.so: cannot open shared object file: No such file or directory

I also am not sure if we should set this in a project's .cargo/config.toml; these settings might be more appropriate in the user's global configuration ($CARGO_HOME/config.toml).