Update ecosystem.adoc with DbVisualizer SQL client for Cassandra

[BloomBoy]

We added our sql tool DbVisualizer that has extended support for Cassandra object types to the Ecosystem page.

[michaelsembwever]

This PR looks good.

But your page ( https://www.dbvis.com/database/cassandra/ ) is in trademark violation of the project. Can you please make a few trivial edits to this page to correct this.

The project's formal name is "Apache Cassandra®", and this formal name must be used the first time it appears on the page, and in any title or header line. The registered trademark symbol is also important to include in this initial use. Subsequent usages can then use the shortened informal "Cassandra". In addition pages that use the product name must add the trademark attribution footer, somewhere on their page.

Like:

Apache, Apache Cassandra, Cassandra, are either registered trademarks or trademarks of the Apache Software Foundation.

This is documented in more detail at https://www.apache.org/foundation/marks
This applies to all Apache projects, wherever you may reference them.

Again, changes requested here are very minimal, not more than a few minutes work. If there's any questions or confusion at all, I will be more than happy to help.

The project, and the foundation, are made up of volunteers, and we always need help catching these innocent mistakes on other websites.