Lazy connect to config_db during first collect instead of during init

[tirupatihemanth]

Why I did it

Avoid reading CONFIG_DB when sonic-hostservice initializes. On DPU boot, the host service can start before database files are ready, causing a transient parseDatabaseConfig error even though artifact collection is not requested yet.

Observed log:

2026 Jul  7 09:27:01.087175 sonic INFO systemd[1]: Started sonic-hostservice.service - SONiC Host Service.
2026 Jul  7 09:27:01.092005 sonic ERR python3: :- parseDatabaseConfig: Sonic database config file doesn't exist at /var/run/redis/sonic-db/database_config.json
2026 Jul  7 09:27:01.095411 sonic INFO python3[1218]: Failed to read hostname/board_type from CONFIG_DB: Sonic database config file doesn't exist at /var/run/redis/sonic-db/database_config.json
2026 Jul  7 09:27:08.163389 sonic INFO systemd[1]: Starting database.service - Database container...

Work item tracking

• Microsoft ADO (number only): N/A

How I did it

• Initialize debug artifact metadata with safe defaults in DebugArtifactCollector.__init__.
• Keep CONFIG_DB metadata lookup lazy during the first collect() call.
• Add a unit test to ensure constructor initialization does not read device metadata.

How to verify it

• Run tests/debug_info_test.py.
• Restart sonic-hostservice before database readiness and verify init emits no parseDatabaseConfig error.

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202012
• 202106
• 202111
• 202205
• 202211
• 202305
• 202311
• 202405
• 202411
• 202605

Reason: fixes a DPU boot-time false error log.

Tested branch (Please provide the tested image version)

• 202605
• master

Description for the changelog

Lazy connect to config_db during first collect instead of during init

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[hdwhdw]

Just confirmed it safe since this is the default value the collect function as well. But I'll recommend creating a constant for it so we know this is the default value and not some random string.

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[tirupatihemanth]

@hdwhdw thanks for the review. Addressed the concern in the new revision. Please take a look.