Merge ALTER TABLE ddl with CREATE TABLE in case of Primary Key, Unique and Check Constraints

[sanyamsinghal]

Describe the changes in this pull request

TODO: Disable the feature.

• Added a new transformer struct with method MergeConstraints(). In future we can add more to it.

• the new table.sql won't have ALTER TABLE ADD CONSTRAINT ddl in case of Primary Key, Unique and Check Constraints
  For example: the following ALTER ddls will be merged with CREATE

• Performance Improvement - This change will reduce the time to half (2x improvement) for cases where PK is in a separate ALTER TABLE ddl than CREATE TABLE

     CREATE TABLE all_constraints (
         col1 INT,
         col2 TEXT
     );
	-- CHECK Constraint
    ALTER TABLE all_constraints
        ADD CONSTRAINT c_ck CHECK (col1 > 0);

    -- PRIMARY KEY Constraint
    ALTER TABLE all_constraints
        ADD CONSTRAINT c_pk PRIMARY KEY (col1);

    -- UNIQUE Constraint
    ALTER TABLE all_constraints
        ADD CONSTRAINT c_uk UNIQUE (col2);
        
    -- Above 4 DDLs will be merged into 1
     CREATE TABLE all_constraints (
           col1 int, 
           col2 text, 
           CONSTRAINT c_ck CHECK (col1 > 0), 
           CONSTRAINT c_pk PRIMARY KEY (col1), 
           CONSTRAINT c_uk UNIQUE (col2)
     );

Describe if there are any user-facing changes

table.sql file will contain fewer ALTER table ddls.

How was this pull request tested?

Added Unit tests.
Existing end to end tests are enough.
Verified with some end to end tests also.

Does your PR have changes that can cause upgrade issues?

Component	Breaking changes?
MetaDB	No
Name registry json	No
Data File Descriptor Json	No
Export Snapshot Status Json	No
Import Data State	No
Export Status Json	No
Data .sql files of tables	No
Export and import data queue	No
Schema Dump	Yes (table.sql will contain lesser DDLs)
AssessmentDB	No
Sizing DB	No
Migration Assessment Report Json	No
Callhome Json	No
YugabyteD Tables	No
TargetDB Metadata Tables	No

[sanyamsinghal]

For Oracle and postgres complex schema tests

• https://jenkins.dev.yugabyte.com/job/users/job/yb-voyager-testing/job/yb-voyager-testing-pipeline/4754/
• Rebuild: https://jenkins.dev.yugabyte.com/job/users/job/yb-voyager-testing/job/yb-voyager-testing-pipeline/4761/

[makalaaneesh]

Yet to review tests.

[sanyamsinghal]

https://jenkins.dev.yugabyte.com/job/users/job/yb-voyager-testing/job/yb-voyager-testing-pipeline/4771/

[makalaaneesh]

LGTM with a nit.

[sanyamsinghal]

Before Disabling: https://jenkins.dev.yugabyte.com/job/users/job/yb-voyager-testing/job/yb-voyager-testing-pipeline/4772/
After disabling: https://jenkins.dev.yugabyte.com/job/users/job/yb-voyager-testing/job/yb-voyager-testing-pipeline/4773/