SDK search index improvements (tracking issue)

[isoos]

• Index content should be downloaded at the time we create the docker image, reduces the isolate startup latencies.
• We should consider using a separate isolate for the SDK index, can be a fixed one after the content doesn't need a reload.
• We should track latencies separately, optionally skipping the index if otherwise latencies are high.
• Consider merging the two SDK index and search them only a single time instead of sequentially.