Removes `testenv` annotations and related code. These annotations originally let you skip x-pack snippet tests in the docs. However, that's no longer possible.
Relates to #79309, #31619
Changes:
* Swaps the `dev` admonitions for `experimental` admonitions
* Removes `ifdef` statements preventing the docs from appearing in
released branches
Changes:
* Documents the `size` default as `10`.
* Updates `size` param def to note its relation to pipes.
* Updates the `head` and `tail` pipe docs to modify sequences.
* Documents the `fetch_size` parameter.
Relates to #59014 and #59063
James Rodewig
James Rodewig