Add support for config fragments

[LaurentGoderre]

Using this approach, you can easily override our custom settings or add your own like this:

services:
  redis:
    image: redis:test
    configs:
      - source: redis_config
        target: /usr/local/etc/redis/conf.d/my.conf

configs:
  redis_config:
    content: |
      port 8000

Which yields

[+] Running 2/0
 ✔ Network redis_default    Created                                                                                                                                                                        0.0s 
 ✔ Container redis-redis-1  Created                                                                                                                                                                        0.0s 
Attaching to redis-1
redis-1  | 1:C 06 Feb 2025 21:16:42.399 * oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
redis-1  | 1:C 06 Feb 2025 21:16:42.399 * Redis version=7.4.2, bits=64, commit=00000000, modified=0, pid=1, just started
redis-1  | 1:C 06 Feb 2025 21:16:42.399 * Configuration loaded
redis-1  | 1:M 06 Feb 2025 21:16:42.399 * monotonic clock: POSIX clock_gettime
redis-1  | 1:M 06 Feb 2025 21:16:42.399 * Running mode=standalone, port=8000.
redis-1  | 1:M 06 Feb 2025 21:16:42.400 * Server initialized
redis-1  | 1:M 06 Feb 2025 21:16:42.400 * Ready to accept connections tcp