Documented the query cache module

Related to #7161 and #7167
[TEST] Assert that put mappings requests are acked in GeoMappingTests.
[TEST] fixed unicast bw comp test configuration

The second internal node, when present, wasn't able to join the existing cluster due ti misconfigured unicast hosts, thus it would form its own cluster.
Internal: fixed typo in NodeService s/disovery/discovery
REST spec: Added missing query_cache param to clear_cache, nodes.stats and indices.stats

Relates to #7167 and #7161
Test: Trimmed trailing whitespace to make valid YAML
Tidied up the filters agg docs and added a coming[] tag
[DOCS] fixed title for filters aggregation documentation
Add tests for corrupted translog files
WIP for where to read and write translog header
make the recovery translog rename retries into a constant instead of a
magic number
Move readSource into Translog instead of making it a TranslogStreams method
docs
getStream() implementation
add TODO about needing versioning
Start with NewTranslogStreams giving VersionedTranslogStreams
TranslogStreamVersion0 should write the size header
What is this I don't even
collapse .hasNext() and .next() into single .next() method
Use .seekTo() instead of .seekForward()