cdc: separate schema and topic prefix for changefeed namespace

[amruss]

Is your feature request related to a problem? Please describe.
When one kafka cluster is used for many changefeeds, with the same table name, the client cannot differentiate between changefeeds.

Describe the solution you'd like
Change the namespace of the changefeed for the schema and topic. Add a flag (WITH option) where we’ll use fully qualified name (topic+schema) for given table rather than just table name. Default behavior is just table name.

Describe alternatives you've considered
Should add schema prefix OR topic prefix as schema name -- fine with either
Either:

• Prefix the schema namespace with what we use for topic namespace, or
• User can specify prefix used in both

Additional context
Could also solve #28670

[blathers-crl]

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[amruss]

Options for command UX

Option 1
CREATE CHANGEFEED FOR INTO ‘kafka://endpoint?topic_prefix=X&schema_prefix=Y’ WITH fully_qualified_name

Schema namespace:
<schema_prefix>..<database_schema>.<table_name>

Topic namespace:
<topic_prefix>..<database_schema>.<table_name>

Option 2
CREATE CHANGEFEED FOR INTO ‘kafka://endpoint?topic_prefix=X’ WITH fully_qualified_name

Schema namespace:
<topic_prefix>..<database_schema>.<table_name>

Topic namespace:
<topic_prefix>..<database_schema>.<table_name>

Option 3
CREATE CHANGEFEED FOR INTO ‘kafka://endpoint?topic_prefix=X&schema_prefix=topic_prefix’ WITH fully_qualified_name

Schema namespace:
<schema_prefix>..<database_schema>.<table_name>

Topic namespace:
<topic_prefix>..<database_schema>.<table_name>

Option 4
CREATE CHANGEFEED FOR INTO ‘kafka://endpoint?topic_and_schema_prefix=X’ WITH fully_qualified_name

Schema namespace:
<topic_and_schema_prefix>..<database_schema>.<table_name>

Topic namespace:
<topic_and_schema_prefix>..<database_schema>.<table_name>