Add Unit testing for the Hot-Reload dependencies

[aaronburtle]

As a part of Hot Reload, we refresh a set of objects that depend on the config at startup. To better validate that this refresh process works correctly, we need to add testing that demonstrates these objects are refreshed correctly. The objects come from the following classes:

QueryManagerFactory
MetadataProviderFactory
QueryEngineFactory
MutationEngineFactory
QueryExecutor
MsSqlQueryExecutor
MySqlQueryExecutor
PostgreSqlQueryExecutor
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