Serialize reference table modifications with node changes & restore point

With Citus MX enabled, when a reference table is modified, it does
some operations on the first worker node(e.g., acquire locks).

If node metadata is locked (via add node or create restore point),
the changes to the reference tables should be blocked.

src/test/regress/expected/isolation_add_node_vs_reference_table_operations.out

@@ -25,10 +25,11 @@ step s1-add-second-worker:
 
 step s2-copy-to-reference-table:
 	COPY test_reference_table FROM PROGRAM 'echo 1 && echo 2 && echo 3 && echo 4 && echo 5';
-
+ <waiting ...>
 step s1-commit: 
     COMMIT;
 
+step s2-copy-to-reference-table: <... completed>
 step s2-print-content:
 	SELECT
 		nodeport, success, result
@@ -69,15 +70,16 @@ step s2-copy-to-reference-table:
 
 step s1-add-second-worker:
 	SELECT 1 FROM master_add_node('localhost', 57638);
+ <waiting ...>
+step s2-commit: 
+	COMMIT;
 
+step s1-add-second-worker: <... completed>
 ?column?
 ---------------------------------------------------------------------
        1
 (1 row)
 
-step s2-commit:
- COMMIT;
-
 step s2-print-content:
 	SELECT
 		nodeport, success, result
@@ -123,10 +125,11 @@ step s1-add-second-worker:
 
 step s2-insert-to-reference-table:
 	INSERT INTO test_reference_table VALUES (6);
-
+ <waiting ...>
 step s1-commit: 
     COMMIT;
 
+step s2-insert-to-reference-table: <... completed>
 step s2-print-content:
 	SELECT
 		nodeport, success, result
@@ -167,15 +170,16 @@ step s2-insert-to-reference-table:
 
 step s1-add-second-worker:
 	SELECT 1 FROM master_add_node('localhost', 57638);
+ <waiting ...>
+step s2-commit: 
+	COMMIT;
 
+step s1-add-second-worker: <... completed>
 ?column?
 ---------------------------------------------------------------------
        1
 (1 row)
 
-step s2-commit:
- COMMIT;
-
 step s2-print-content:
 	SELECT
 		nodeport, success, result
@@ -429,10 +433,11 @@ step s1-add-second-worker:
 
 step s2-copy-to-reference-table:
 	COPY test_reference_table FROM PROGRAM 'echo 1 && echo 2 && echo 3 && echo 4 && echo 5';
-
+ <waiting ...>
 step s1-commit: 
     COMMIT;
 
+step s2-copy-to-reference-table: <... completed>
 step s2-print-content:
 	SELECT
 		nodeport, success, result
@@ -470,15 +475,16 @@ step s2-copy-to-reference-table:
 
 step s1-add-second-worker:
 	SELECT 1 FROM master_add_node('localhost', 57638);
+ <waiting ...>
+step s2-commit: 
+	COMMIT;
 
+step s1-add-second-worker: <... completed>
 ?column?
 ---------------------------------------------------------------------
        1
 (1 row)
 
-step s2-commit:
- COMMIT;
-
 step s2-print-content:
 	SELECT
 		nodeport, success, result
@@ -521,10 +527,11 @@ step s1-add-second-worker:
 
 step s2-insert-to-reference-table:
 	INSERT INTO test_reference_table VALUES (6);
-
+ <waiting ...>
 step s1-commit: 
     COMMIT;
 
+step s2-insert-to-reference-table: <... completed>
 step s2-print-content:
 	SELECT
 		nodeport, success, result
@@ -562,15 +569,16 @@ step s2-insert-to-reference-table:
 
 step s1-add-second-worker:
 	SELECT 1 FROM master_add_node('localhost', 57638);
+ <waiting ...>
+step s2-commit: 
+	COMMIT;
 
+step s1-add-second-worker: <... completed>
 ?column?
 ---------------------------------------------------------------------
        1
 (1 row)
 
-step s2-commit:
- COMMIT;
-
 step s2-print-content:
 	SELECT
 		nodeport, success, result

src/test/regress/expected/isolation_create_restore_point.out

@@ -409,15 +409,16 @@ step s1-insert-ref:
 
 step s2-create-restore:
 	SELECT 1 FROM citus_create_restore_point('citus-test');
+ <waiting ...>
+step s1-commit: 
+	COMMIT;
 
+step s2-create-restore: <... completed>
 ?column?
 ---------------------------------------------------------------------
        1
 (1 row)
 
-step s1-commit:
- COMMIT;
-
 
 starting permutation: s1-begin s1-modify-multiple-ref s2-create-restore s1-commit
 create_reference_table
@@ -434,15 +435,16 @@ step s1-modify-multiple-ref:
 
 step s2-create-restore:
 	SELECT 1 FROM citus_create_restore_point('citus-test');
+ <waiting ...>
+step s1-commit: 
+	COMMIT;
 
+step s2-create-restore: <... completed>
 ?column?
 ---------------------------------------------------------------------
        1
 (1 row)
 
-step s1-commit:
- COMMIT;
-
 
 starting permutation: s1-begin s1-ddl-ref s2-create-restore s1-commit
 create_reference_table
@@ -485,15 +487,16 @@ step s1-copy-ref:
 
 step s2-create-restore:
 	SELECT 1 FROM citus_create_restore_point('citus-test');
+ <waiting ...>
+step s1-commit: 
+	COMMIT;
 
+step s2-create-restore: <... completed>
 ?column?
 ---------------------------------------------------------------------
        1
 (1 row)
 
-step s1-commit:
- COMMIT;
-
 
 starting permutation: s1-begin s1-drop-ref s2-create-restore s1-commit
 create_reference_table