Fix multiple, successive connections using AKV provider

[David-Engel]

Previously, the test added in this PR would throw the following error on the second connection attempt within the same process when using the built-in AKV key store provider via connection string options:

com.microsoft.sqlserver.jdbc.SQLServerException: Key store providers cannot be set more than once.
	at com.microsoft.sqlserver.jdbc.SQLServerConnection.registerColumnEncryptionKeyStoreProviders(SQLServerConnection.java:859)
	at com.microsoft.sqlserver.jdbc.SQLServerConnection.registerKeyVaultProvider(SQLServerConnection.java:1606)
	at com.microsoft.sqlserver.jdbc.SQLServerConnection.registerKeyStoreProviderOnConnection(SQLServerConnection.java:1580)
	at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectInternal(SQLServerConnection.java:1844)
	at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(SQLServerConnection.java:1469)
	at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(SQLServerDriver.java:921)
	at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)
	at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:251)
	at jdbctest.jdbctest.GenericTests(jdbctest.java:45)
	at jdbctest.jdbctest.main(jdbctest.java:26)

[lilgreenbird]

/azp run Microsoft.mssql-jdbc.macOS

[azure-pipelines]

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