fix: report clearer error message when AVG used with DELIMITED

[big-andy-coates]

Description

See #4294

AVG doesn't work with DELIMITED format and the error message isn't great.

Example statements that cause the error:

-- Given:
CREATE STREAM INPUT (VALUE integer) WITH (kafka_topic='test_topic', value_format='DELIMITED');

-- When:
CREATE TABLE OUTPUT AS SELECT avg(value) AS avg FROM INPUT group by ROWKEY;

Old error message:

ksql> CREATE TABLE OUTPUT AS SELECT avg(value) AS avg FROM INPUT group by ROWKEY;
CREATE TABLE OUTPUT AS SELECT avg(value)Value format does not support value schema.
format: DELIMITED
schema: Persistence{schema=STRUCT<KSQL_INTERNAL_COL_0 INT, KSQL_INTERNAL_COL_1 VARCHAR, KSQL_AGG_VARIABLE_0 STRUCT<SUM INT, COUNT BIGINT>> NOT NULL, unwrapped=false}
reason: The 'DELIMITED' format does not support type 'STRUCT'
Caused by: The 'DELIMITED' format does not support type 'STRUCT'

This PR improves the error message a bit:

New error message:

One of the functions used in the statement has an intermediate type that the value format can not handle. Please remove the function or change the format.
Consider up-voting https://github.com/confluentinc/ksql/issues/3950, which will resolve this limitation
Caused by: Value format does not support value schema.
format: DELIMITED
schema:
	Persistence{schema=STRUCT<KSQL_INTERNAL_COL_0 INT, KSQL_INTERNAL_COL_1 VARCHAR,
	KSQL_AGG_VARIABLE_0 STRUCT<SUM INT, COUNT BIGINT>> NOT NULL,
	unwrapped=false}
reason: The 'DELIMITED' format does not support type 'STRUCT'
Caused by: The 'DELIMITED' format does not support type 'STRUCT'

Testing done

manual, unit and QTT.

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[spena]

LGTM