Source versioning: Postgres, MySQL and Load generator

[bobbyiliev]

Initial implementation for the source versioning refactor as per #646

The main changes to consider:

• Marking the table attribute as optional and deprecated for both the MySQL and Postgres sources
• Introduced a new all_tables bool attribute for the MySQL and the Loadgen sources, as in the past this was defaulting always using FOR ALL TABLES in the load gen sources (auction, marketing, tpch) and in the MySQL case whenever no table blocks were defined, we defaulted to FOR ALL TABLES. This all_tables bool attribute allows us to create sources without any tables defined as per the source versioning work
• Introducing the new materialize_source_table_{mysql|postgres|load_generator} resource which allows us to do CREATE TABLE ... FROM SOURCE ...

Things that are still pending: https://github.com/MaterializeInc/terraform-provider-materialize/issues/646

[rjobanp]

@morsapaes @bobbyiliev let's discuss this PR at the sources & sinks meeting this week - we should decide when it makes sense to merge this - my thinking is we should do so whenever we move into private preview for the source versioning feature. But if we want to merge sooner and just have a disclaimer that the things mentioned as 'deprecated' here are not actually yet deprecated, that could work too

[bobbyiliev]

One thing that we can consider here as per this old tracking issue: https://github.com/MaterializeInc/terraform-provider-materialize/issues/391 is take the chance and decide if we still want to rename some of the attributes in the new source table resources:

Lists For attributes that use list, we have more cases of singular than plural.	Attribute	Resource	Type	Plural	Comment
start_offset	materialize_source_kafka	List of Strings		In Materialize the attribute is singular START OFFSET even though it is a list of strings
header	materialize_source_kafka	List of Strings		In Materialize the attribute is singular HEADER even though it is a list of strings
text_columns	materialize_source_postgres	List of Strings	X

Blocks We had decided should be singular. There are some blocks that use plural so this could be a good chance to rename those attributes in the new source table load gen resource:	Attribute	Resource	Type	Plural
auction_options	materialize_source_load_generator	Block	X
counter_options	materialize_source_load_generator	Block	X
marketing_options	materialize_source_load_generator	Block	X
tpch_options	materialize_source_load_generator	Block	X
check_options	materialize_webhook	Block	X