Add validate method to MultiTableMetadata

[amontanez24]

Problem Description

As a user, it would be useful to make sure the multi-table metadata I've specified is formatted correctly.

Expected behavior

• Add a validate method
• The validation should have 2 steps
  1. First, run the SingleTableMetadata.validate method for each table and group the error messages.
  2. Validate the relationships (described in detail in the Additional context section)
• If any errors show it should raise a InvalidMetadataError with all of the errors grouped by table

>>> metadata.validate()
InvalidMetadataError: The metadata is not valid

Table: 'users'
Error: Invalid values ("pii") for datetime column "start_date".
Error: A Unique constraint is being applied to column "age". This column is already a key for that table.

Table: 'transactions'
Error: Invalid regex format string "[A-{6}" for text column "transaction_id"
Error: Unknown key value 'ttid'. Keys should be columns that exist in the table.
Error: Invalid increment value (0.5) in a FixedIncrements constraint. Increments must be positive integers.

Relationships:
Error: Relationship between tables ('users', 'transactions') contains an unknown primary key 'userr_id'.
Error: The relationships in the dataset are disjointed. Tables ('sessions') are not connected to any of the other tables.

Additional context

Relationship validation

• "parent_table_name" and "child_table_name" should refer to tables that are defined in the "tables" portion of the metadata
  Error: Relationship contains an unknown table 'userss'.

• "parent_primary_key" value should be the same as "primary_key" in the table definition
  Error: Relationship between tables ('users', 'transactions') contains an unknown primary key 'userr_id'.

• "child_foreign_key" should refer to column(s) that are defined in the "tables" portion of the metadata
  Error: Relationship between tables ('users', 'transactions') contains an unknown foreign key 'transactions_idd'.

• The length of "child_foreign_key" should match the length of "parent_primary_key" (you cannot have a single column foreign key referencing a multi-column composite primary key)
  Error: Relationship between tables ('users', 'transactions') is invalid. Primary key has length 2 but the foreign key has length 1.

• The sdtype & attributes of the primary key should exactly match the sdtype & attributes of the foreign key
  Error: Relationship between tables ('users', 'transactions') is invalid. The primary and foreign key columns are not the same type.

  • If it's a composite key then match by the order in the list; eg. check that the 0-index has the same definitions, then the 1-index

• The relationships should be acyclic (eg. you cannot have a cycle of dependencies A → B → C → A)
  Error: The relationships in the dataset describe a circular dependency between tables ('users', 'sessions', 'transactions').

• All tables in the metadata must be connected. Only need to throw a max of 1 error of this type.
  Error: The relationships in the dataset are disjointed. Tables ('users') are not connected to any of the other tables.