There is compile time option PACKAGE in cmake to define
current build distribution info. By default it's
"Tarantool" for the community version and "Tarantool Enterprise"
for the enterprise version.

It's displayed in console greeting and in `box.info().package`,
but, unfortunately, it can't be accessed from Lua before `box.cfg`.

This patch exposes `require('tarantool').package`.

Close #4408

@TarantoolBot document
Title: Extend module "tarantool" with the field "package"

Beside from build info and version, module "tarantool" now provides
"package" field. By default it equals string "Tarantool", but
can differ for other distributions like "Tarantool Enterprise".

Example:

```console
tarantool> require('tarantool')
---
- version: 2.3.0-3-g302bb3241
  build:
    target: Linux-x86_64-RelWithDebInfo
    options: cmake . -DCMAKE_INSTALL_PREFIX=/opt/tarantool-install
-DENABLE_BACKTRACE=ON
    mod_format: so
    flags: ' -fexceptions -funwind-tables -fno-omit-frame-pointer
-fno-stack-protector
      -fno-common -fopenmp -msse2 -std=c11 -Wall -Wextra
-Wno-strict-aliasing -Wno-char-subscripts
      -Wno-format-truncation -fno-gnu89-inline -Wno-cast-function-type'
    compiler: /usr/bin/cc /usr/bin/c++
  pid: 'function: 0x40016cd0'
  package: Tarantool
  uptime: 'function: 0x40016cb0'
...

```