wip: Add EndpointTraceItemStats RPC

[shruthilayaj]

requires getsentry/sentry-protos#101

For comparison workflows, we need the count distribution data of all attribute/value pairs (both string and numeric, however we'll focus on string first). We're introducing a trace item stats endpoint to facilitate that. The aim is to build a somewhat generic endpoint that can give a high level overview of the shape of your data.

This implementation is fairly simple, restricted to string attributes to begin with. It returns the frequency distribution of attributes in the requested filter. The data returned is ordered by keys that have the highest frequency attribute values.

[shruthilayaj]

SELECT
    (arrayJoin(mapConcat(attr_str_0, attr_str_1, attr_str_2, attr_str_3, attr_str_4, attr_str_5, attr_str_6, attr_str_7, attr_str_8, attr_str_9, attr_str_10, attr_str_11, attr_str_12, attr_str_13, attr_str_14, attr_str_15, attr_str_16, attr_str_17, attr_str_18, attr_str_19) AS attr_str_concat) AS attr_str).1 AS attr_keys,
    attr_str.2 AS attr_values,
    sumIf(sign * sampling_weight, ((duration_micro / 1000) AS `sentry.duration_ms`) IS NOT NULL) AS count
FROM eap_spans_2_local
WHERE (project_id IN [1, 2, 3]) AND (organization_id = 1) AND less(_sort_timestamp, toDateTime(1737500400)) AND greaterOrEquals(_sort_timestamp, toDateTime(1737489600)) AND true
GROUP BY
    attr_keys,
    attr_values
ORDER BY count DESC
LIMIT 10 BY attr_keys
LIMIT 0, 100

the resulting query looks like this ^
https://www.notion.so/sentry/Naive-approach-for-stats-endpoint-1848b10e4b5d80708bcffa341e0f225a
ran this query locally and on snuba admin, documented results - snuba admin is being a little buggy so couldn't do something more comprehensive