Field caps request returns too much data

[lightindigo]

After changes introduced in #20, when w're trying to request logs from otel indices for a large period eg 30 days, request for _field_caps either takes a lot of time, holding logs request or even fails due to its response size, because attributes.* field may return infinite amount of fields due to it's highly dynamic nature. I believe it would be nice to have ability to either disable the autocomplete feature for specific datasource or have ability to pick fields/index source for autocomplete to make better experience here.

[pbasgod7]

We're experiencing the same issue with our logs indices in Grafana 12.4.0 using the Quickwit datasource plugin v0.6.0.

Symptoms:

• _field_caps responses are extremely large (up to 57 MB for a single request)
• Request times are 30+ seconds, often timing out
• Frequent 500 errors when querying larger time ranges
• This significantly impacts the user experience when browsing logs

Example network traffic:

_field_caps?start_timestamp=1776014007&end_timestamp=1778606008    200    57,172 kB    30.75 s
_field_caps?start_timestamp=1776013746&end_timestamp=1778605747    500    0.4 kB      30.05 s
_field_caps?start_timestamp=1776013716&end_timestamp=1778605717    500    0.4 kB      30.03 s

The root cause appears to be highly dynamic fields generating an enormous number of field mappings.

Feature request:
Would greatly appreciate the ability to:

1. Disable field_caps entirely via datasource configuration, or
2. Filter/limit which fields are included in field_caps responses
3. Cache field_caps results with configurable TTL