Readme for CORE-5887 (Allow the use of management statements in PSQL blocks).

doc/sql.extensions/README.management_statements_psql.md

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+# Management Statements in PSQL
+
+Before Firebird 4, management statements were not allowed inside PSQL blocks. They were allowed only as top-level SQL statements, or as top-level statement of an EXECUTE STATEMENT embedded in a PSQL block.
+
+Now they are allowed inside PSQL blocks (triggers, procedures, execute block) directly.
+
+As many applications depends that some management statements be issued on the connection start, ON CONNECT triggers is a good place to put them in this situation.
+
+The management statements part of this improvement are:
+- ALTER SESSION RESET
+- SET DECFLOAT ROUND
+- SET DECFLOAT TRAPS TO
+- SET DECFLOAT BIND
+- SET ROLE
+- SET SESSION IDLE TIMEOUT
+- SET STATEMENT TIMEOUT
+- SET TIME ZONE
+- SET TIME ZONE BIND
+- SET TRUSTED ROLE
+
+## Examples
+
+```sql
+create or alter trigger on_connect on connect
+as
+begin
+    set decfloat bind double precision;
+    set time zone 'America/Sao_Paulo';
+end
+```