Deprecate & remove serializeTargetValueType

[not-napoleon]

In #42949 we removed all use of target value type in the subclasses of ValuesSourceAggregationBuilder, but left the serialization format sending a hard-coded null to preserve compatibility. This ticket tracks the work of removing that null from the serialization format, and the associated logic in VSAB.

[elasticmachine]

Pinging @elastic/es-analytics-geo (:Analytics/Aggregations)

[kaliljoao]

Hi guys, I would like to work on this issue.

[not-napoleon]

@kaliljoao Sounds good, let me know if you need any help! (Sorry for the slow reply - I was out of office last week)

[kaliljoao]

@kaliljoao Sounds good, let me know if you need any help! (Sorry for the slow reply - I was out of office last week)

Hey @not-napoleon, can U help me? I started my work on this issue today and I am confused about what exactly I need to do. Do I need only to remove where null was hard-coded? My doubt was caused because it is just one line of code, if I am not wrong of course.

[not-napoleon]

@kaliljoao You're right, it is only a couple of lines of code. The difficulty is that we need to maintain backwards compatibility and carefully deprecate this method. You need to detect the target version (we have some tools for this) and adapt the wire format accordingly. Honestly, this is a tricky issue and not one I'd really recommend for someone not well versed in how Elasticsearch maintains backwards compatibility. Usually we don't expect community members to deal with that, which is why this wasn't labeled help wanted