Accountsdb plugin transaction part 2: transaction selector (#21331)

Created the transaction_selector which allows the user to configure the transactions to stream:

all transactions
all vote transactions
transactions mentioning accounts

accountsdb-plugin-postgres/src/lib.rs

@@ -1,3 +1,4 @@
 pub mod accounts_selector;
 pub mod accountsdb_plugin_postgres;
 pub mod postgres_client;
+pub mod transaction_selector;