YAML Anchors Not Fully Supported Yet

[kylhuk]

In regards to issue #58

According to the YAML specifications (https://yaml.org/type/merge.html), the following merge variants are valid:

- # Merge one map
  << : *CENTER

- # Merge multiple maps
  << : [ *CENTER, *BIG ]

Variant number 1 seems to be supported now because of k9withabone/compose_spec_rs#2

However, variant number 2 seems to cause issues.

Error log:

Error: 
   0: error converting compose file
   1: error reading compose file
   2: File `docker-compose.yaml` is not a valid compose file
   3: unknown anchor at line 69 column 11

Location:
   /home/admin/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/podlet-0.3.0/src/cli/compose.rs:203

  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ BACKTRACE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
   1: color_eyre::config::EyreHook::into_eyre_hook::{{closure}}::heb83b7ecd99b6378
      at <unknown source file>:<unknown line>
   2: eyre::capture_handler::h2d5f2a58549e90ee
      at <unknown source file>:<unknown line>
   3: eyre::error::<impl eyre::Report>::from_msg::h066738ed4de690b7
      at <unknown source file>:<unknown line>
   4: podlet::cli::compose::Compose::try_into_files::h933401fdb1913013
      at <unknown source file>:<unknown line>
   5: podlet::cli::Cli::try_into_files::h7abb95bd96550b46
      at <unknown source file>:<unknown line>
   6: podlet::cli::Cli::print_or_write_files::h7d2c0f81561e5663
      at <unknown source file>:<unknown line>
   7: podlet::main::h87393c11d805095a
      at <unknown source file>:<unknown line>
   8: std::sys::backtrace::__rust_begin_short_backtrace::hc69a0508aa052acd
      at <unknown source file>:<unknown line>
   9: std::rt::lang_start::{{closure}}::h30a74f0c3d770230
      at <unknown source file>:<unknown line>
  10: std::rt::lang_start_internal::h31bbb7f936fd6b5d
      at <unknown source file>:<unknown line>
  11: main<unknown>
      at <unknown source file>:<unknown line>
  12: __libc_start_main<unknown>
      at <unknown source file>:<unknown line>
  13: _start<unknown>
      at <unknown source file>:<unknown line>

YAML file docker-compose.yaml

x-stdin-tty: &stdin-tty
  stdin_open: true
  tty: true

x-container-default: &container-default
  <<: *stdin-tty
  networks:
    - custom

x-resource-high: &resource-high
  deploy:
    resources:
      limits:
        cpus: '7.0' # Limit to 50% of a CPU
        memory: 12G # Limit to 256 megabytes of RAM
      reservations:
        memory: 5G # Reserve 128 megabytes of RAM

x-dns: &dns
  dns:
    - 192.168.72.1
    - 9.9.9.9

services:
  sonarr:
    container_name: "sonarr"
    <<: [ *x-container-default, *x-resource-high, *x-dns ]
    image: linuxserver/sonarr:latest
    environment:
      - TZ=${TZ} # timezone, defined in .env
    volumes:
      - /etc/localtime:/etc/localtime:ro
      - sonarr:/config # config files
      - lama-nas-tvshows:/tv # tv shows folder
#      - lama-nas-downloads:/downloads # download folder
      - sabnzbd-downloads:/downloads
    ports:
      - 8989:8989

# config for volumes has been omitted as it is not relevant in this case