lua-yaml: improve multiline string output

Added tarantool.compat option that allows yaml.encode() to encodes all
strings containing a newline in a more convenient block scalar style.
This is a breaking change, programs that rely on precise lyaml encoding
may fail if the new behavior is selected.

Closes #3012
Requires #7060
Requires #8007

@TarantoolBot document
Title: YAML formatter improvement

Now yaml.encode() can encode strings with a newline in block scalar style,
see https://yaml.org/spec/1.2-old/spec.html#style/block/literal and
https://github.com/tarantool/tarantool/wiki/compat%3Ayaml_pretty_multiline

old:
```
tarantool> compat.yaml_pretty_multiline = 'old'
---
...

tarantool> return "Title: xxx\n- Item 1\n- Item 2\n"
---
- 'Title: xxx

  - Item 1

  - Item 2

  '
...

```

new:
```
tarantool> compat.yaml_pretty_multiline = 'new'
---
...

tarantool> return "Title: xxx\n- Item 1\n- Item 2\n"
---
- |
  Title: xxx
  - Item 1
  - Item 2
...

```