Have `freshness_rules` optional for Tables

[vicmattos]

Scenario

I have a source wide freshness configuration (outside of tables key) with warn_after for 2 days and error_after for 3.

There's one table in this source definition that would like to configure to alert me only after 30 days, so I overwrite the source wide config only for that.

Since it's a big timeframe, would like to get an error without the warning.

version: 2

sources:
  - name: schema_name
    
    freshness:
      warn_after: {count: 2, period: day}
      error_after: {count: 3, period: day}

    tables:
      - name: table_name
        freshness:
          warn_after:
          error_after: {count: 30, period: day}

Current State

The empty key warn_after returns the error Incorrect type. Expected "freshness_rules".

Proposal

Make the freshness_rules optional for table freshness