Prevent usage of time_bucket_ng in CAgg definition

[jnidzwetzki]

The function timescaledb_experimental.time_bucket_ng() has been
deprecated for two years. This PR removes it from the list of bucketing
functions supported in a CAgg. Existing CAggs using this function will
still be supported; however, no new CAggs using this function can be
created.

---

I added a GUC, that is only available in debug builds (similar to debug_require_batch_sorted_merge), to allow the creation of CAggs using time_bucket_ng. This GUC allows it to prove that existing CAggs using this bucket function continue to work. In addition, this GUC can be used in a further PR to introduce and test migration steps.

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 80.92%. Comparing base (59f50f2) to head (0b6342c).
Report is 94 commits behind head on main.

Files	Patch %	Lines
tsl/src/continuous_aggs/common.c	61.53%	0 Missing and 5 partials ⚠️
src/ts_catalog/continuous_agg.c	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6798      +/-   ##
==========================================
+ Coverage   80.06%   80.92%   +0.85%     
==========================================
  Files         190      194       +4     
  Lines       37181    36863     -318     
  Branches     9450     9653     +203     
==========================================
+ Hits        29770    29830      +60     
- Misses       2997     3180     +183     
+ Partials     4414     3853     -561     

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[akuzm]

How does it work during upgrade, will people be able to upgrade if they have such caggs?

[jnidzwetzki]

This function is only called when you create new CAggs. So, this PR blocks only the ability to create new CAggs using time_bucket_ng. Existing CAggs continue to work.

-- 2.14.2
CREATE MATERIALIZED VIEW conditions_summary_weekly
WITH (timescaledb.continuous, timescaledb.materialized_only=true) AS
SELECT city,
       timescaledb_experimental.time_bucket_ng('7 days', day, '2000-01-03' :: date) AS bucket,
       MIN(temperature),
       MAX(temperature)
FROM conditions
GROUP BY city, bucket
WITH NO DATA;

test1=# select * from _timescaledb_catalog.continuous_aggs_bucket_function ;
 mat_hypertable_id |                         bucket_func                         | bucket_width | bucket_origin | bucket_offset | bucket_timezone | bucket_fixed_width
-------------------+-------------------------------------------------------------+--------------+---------------+---------------+-----------------+--------------------
                 2 | timescaledb_experimental.time_bucket_ng(interval,date,date) | 604800000000 |               |               |                 | t
(1 row)


test1=# alter extension timescaledb update;
ALTER EXTENSION

INSERT into conditions values(now(), 'Hamburg', 34);
CALL refresh_continuous_aggregate('conditions_summary_weekly', NULL, NULL);

-- 2.15.0-dev
CREATE MATERIALIZED VIEW conditions_summary_weekly2
WITH (timescaledb.continuous, timescaledb.materialized_only=true) AS
SELECT city,
       timescaledb_experimental.time_bucket_ng('7 days', day, '2000-01-03' :: date) AS bucket,
       MIN(temperature),
       MAX(temperature)
FROM conditions
GROUP BY city, bucket
WITH NO DATA;

ERROR:  experimental bucket functions are not supported inside a CAgg definition
HINT:  Use a function from the _timescaledb_functions schema instead.