[DOCS] fixed count docs, it now requires a top-level query object, same as other apis

Relates to #4074
Fix typo in similarity docs

DRF similarity -> DFR similarity
Allow specifying nested fields in simple_query_string

Fixes #5091
[docs] fixed errors in aggs docs
- error in nested aggs example
- error in terms aggs example
[TEST] added missing wait for yellow in put warmer REST test
Added the `DistanceUnit.NAUTICALMILES` enumeration
label with the corresponding *NM* and *nmi* unit
suffixes. Update the docs to match.

Closes #5085
Update get.asciidoc

Minor improvements.

curl -XHEAD doesn't actually print anything so I've changed to use -I which actually prints the headers received.
[DOCS] improved get docs

- added _version to response
- exists call use -XHEAD with -i flag to include headers in the output
Make sure that parent type is created explicitly.
Cleaned up the p/c integration tests to use shorter mapping definition, ensureGreen() and .get()
Fixed issue where highlighting in percolate existing doc api doesn't work (no highlight snippets)
enable percolation for nested documents
cleanup nested percolator
remove BufferedReader and add tests
add comments and license header
remove custom MemoryIndex, it is never reset anyway
add java test for nested percolator