feature: added the ngx.configure module and APIs

[thibaultcha]

I hereby granted the copyright of the changes in this pull request
to the authors of this lua-resty-core project.

Sister PR of openresty/lua-nginx-module#1259

FFI-based API for dynamic NGINX configuration via a new configure_by_lua phase.

Synopsis:

http { configure_by_lua_block { local ngx_configure = require "ngx.configure" -- hard-coded, but could be retrieved from I/O or env local shms = { { "dogs", "12k" }, { "cats", "24k" } } -- create shms for _, shm in ipairs(shms) do ngx_configure.shared_dict(shm[1], shm[2]) end -- conditionally expose env variables for workers ngx_configure.env("PROXY_PASS_URL") -- configure the Lua VM ngx_configure.max_pending_timers(1024) ngx_configure.max_running_timers(128) } init_by_lua_block { ngx.shared.dogs:set("hello", true) } }