…_ENABLED (#928)

https://datadoghq.atlassian.net/browse/SVLS-7818

  ## Overview
Add DD_LOGS_ENABLED environment variable and YAML config option as an
alias for DD_SERVERLESS_LOGS_ENABLED. Both variables now use OR logic,
meaning logs are enabled if either variable is set to true.

  Changes:
  - Add logs_enabled field to EnvConfig and YamlConfig structs
- Implement OR logic in merge_config functions: logs are enabled if
either DD_LOGS_ENABLED or DD_SERVERLESS_LOGS_ENABLED is true
- Add comprehensive test coverage with 9 test cases covering all
combinations of the two variables
  - Maintain backward compatibility with existing configurations
  - Default value remains true when neither variable is set


## Testing 
Set DD_LOGS_ENABLED and DD_SERVERLESS_LOGS_ENABLED to false and expect:
- [Log can be found in AWS
console](https://us-east-1.console.aws.amazon.com/cloudwatch/home?region=us-east-1#logsV2:log-groups/log-group/$252Faws$252Flambda$252Fltn-fullinstrument-bn-cold-node22-lambda/log-events/2025$252F11$252F13$252F$255B$2524LATEST$255D455478dcbc944055b5be933e2e099f6a$3FfilterPattern$3DREPORT+RequestId)
- [Log could NOT be found in DD
console](https://ddserverless.datadoghq.com/logs?query=source%3Alambda%20%40lambda.arn%3A%22arn%3Aaws%3Alambda%3Aus-east-1%3A425362996713%3Afunction%3Altn-fullinstrument-bn-cold-node22-lambda%22%20AND%20%22REPORT%20RequestId%22&agg_m=count&agg_m_source=base&agg_t=count&clustering_pattern_field_path=message&cols=host%2Cservice%2C%40lambda.request_id&fromUser=true&messageDisplay=inline&refresh_mode=paused&storage=hot&stream_sort=desc&viz=stream&from_ts=1763063694206&to_ts=1763065424700&live=false)

Otherwise the log should be available in DD console.