This changes the validation criteria we use for user and role
names in the file realm, native realm, and the
realm-agnostic code in x-pack security. The new criteria is:
A valid username's length must be at least 1 and no more than 1024
characters. It may not contain leading or trailing whitespace. All
characters in the name must be be alphanumeric (`a-z`, `A-Z`, `0-9`),
printable punctuation or symbols in the https://en.wikipedia.org/wiki/Basic_Latin_(Unicode_block)[Basic Latin (ASCII) block],
or the space character.
Original commit: elastic/x-pack-elasticsearch@f77640f269
855c63dbc7