add yaml-cpp support for file config

[yhmtsai]

This PR adds the yaml-cpp to support yaml format for file config which gives the alias feature to reuse config.
welcome any suggestion of yaml library.

[MarcelKoch]

Regarding the library choice, yaml-cpp seems to be the most popular, but rapidyaml seems to be a good alternative. rapidyaml supports resolving anchors automatically, which would simplify our parse implementation (see here).

[MarcelKoch]

LGTM, only few minor points

[upsj]

LGTM!

[upsj]

I wish there was a better library for YAML parsing, but I guess this will have to do. There are some issues with how yaml-cpp handles assignment and copies jbeder/yaml-cpp#1275. And to quote the developer:

Unfortunately, I don't have time to work on this library any more

Not blocking, just something to keep in mind in case we find a better library out there.

[yhmtsai]

Yes, I also faced the issue that it still accepts the invalid yaml file.
like

arr: &arr1 [1, 2, 3]
base:
  <<: *arr1

which should be invalid because <<: can only used from map not array.
it accepts this file unfortunately.
As @MarcelKoch mentioned, rapidyaml might be another good library to use.
yaml-cpp still served larger group, so I will still merge this first.
Because config is not tied to any specific parse, we can create rapidyaml extension for config later