[DOC]Create documentation for _validate API

[kolchfa-aws]

What do you want to do?

• [ ] Request a change to existing documentation
• [x ] Add new documentation
• [ ] Report a technical problem with the documentation
• [ ] Other

 GET /_validate/query
GET /<index>/_validate/query
POST /_validate/query
POST /<index>/_validate/query

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.