Clarify "What Is Vitess"

[dwelsch-esi]

Overview

Clarify the beginning of the Overview, the "What is Vitess" page.

The introduction to the Overview should describe the nature and purpose of the
product. Readers should be able to guess the components and basic operation
based on the introductory description. The current description (a "database
solution") is vague.

Audience: All

Type: Conceptual

Context

This issue tracks recommended changes resulting from an analysis of the Vitess
documentation commissioned by CNCF. The analysis and supporting documents are
here: https://github.com/cncf/techdocs/tree/main/analyses/0014-vitess.

See the umbrella issue listing all issues identified in the analysis.

Possible Implementation

Related material in the current doc:

• What Is Vitess

Suggested changes:

Rewrite the introductory paragraph of the "What is Vitess" page.

There are already good descriptions elsewhere that would be appropriate.

For example, the introduction from the README in the [code repository][project-website] is pretty good:

Vitess is a cloud-native horizontally-scalable distributed database system
that is built around MySQL.

Or the introduction that this replaced:

Vitess is a database clustering system for horizontal scaling of MySQL through
generalized sharding.