Certain state store components disallow storing empty strings

[ItalyPaleAle]

Description

Originally reported by @mPyKen: #2071 (comment)

Certain state stores are not allowing storing values that are empty strings, which are sometimes used by Dapr Workflows. At a quick glance, the error seems to be returned by:

• Postgres (+ CockroachDB)
• MySQL
• Oracle
• SQLite

It's possible other components have the same issue, even though they may return a separate error message.

We should allow storing empty values, and add a conformance test for that.

Release Note

RELEASE NOTE: FIX Allow storing empty string values in state stores