feat: Expand sql table resource config

[xneg]

Description

It's possible to specify sql table using config.toml file (see docs).

[sources.sql_database.chat_message]
backend="pandas"
chunk_size=1000

[sources.sql_database.chat_message.incremental]
cursor_path="updated_at"

The problem is this setting-based approach allows only append strategy and doesn't allow to specify custom primary or merge keys.
While primary keys are reflected from source table it's not possible for views.
So this PR allows to specify write_disposition, primary_key and merge_key in config.toml file with some restrictions (see Additional Context):

[sources.sql_database.chat_message]
chunk_size=1000

[sources.sql_database.chat_message.incremental]
write_disposition.disposition = "merge"
primary_key = ["id", "updated_at"]
cursor_path="updated_at"

Additional Context

There is a problem with not total alignment between def resource(...) method's arguments and fields in config classes.
Current config system doesn't support Union types (and probably it's not possible and there is no point) but this leads to the situation that we can't use plain string values:

[sources.sql_database.chat_message.incremental]
write_disposition= "merge"
primary_key = "id"

but we have to use more complex dict or lists values:

[sources.sql_database.chat_message.incremental]
write_disposition.disposition= "merge"
primary_key = ["id"]

If you have any better ideas how to realize this opportunity I'm open to adjust my PR or implement it different way.

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