MINOR: add force_reload query parameter to SSL certificate resource p…

…aths

MINOR: add file (full path) attribute to SSL certificate model

FEATURE/MEDIUM: specification: add endpoint to serve OpenAPI v3 spec

Review comments

BUG/MINOR: resolvers: fix field definitions

MINOR: cluster: add path to start certificate refresh

FEATURE/MINOR: server, bind: add allow-0rtt option

BUG/MINOR: validation: ease regex validations

Ease regex validation on backend_switching_rule to allow using
variables for backend name. Also remove regex check for cookie in
backend and defaults to allow adding extra cookie parameters.

MEDIUM: Add info endpoint

MINOR: backend: added hash-type option