What feature or improvement would you like to see?

In the future, we might want to introduce breaking changes to the driver manifest TOML format. Although we don't currently foresee any reason to do this, it's conceivable that we might have good reasons to do it in the future.

If we did this, it could cause older versions of the driver managers to have undefined behavior when reading newer versions of the manifests. Therefore, for safety, we should:

1. Add a manifest version number in the manifest. Set it to integer value 1 for now. For now, this should be an optional field in the manifest, but if it's present, it must be set to 1.
2. In the driver managers, when reading a manifest, always check for a manifest version number, and throw an error if it is present and not equal to 1. The error message should inform the user that the version of their ADBC driver manager is incompatible with the version of the ADBC driver manifest.