fix: persist tedge-container-plugin data by default

[reubenmiller]

Persist the tedge-container-plugin data dir and credentials directory by default by changing the default paths under the container's DATA_DIR.

This ensure that working directory data like docker-compose files are persisted across self updates.

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
21	0	1	21	100	9m10.579358s

Passed Tests

Name	⏱️ Duration	Suite
Supports Cumulocity Basic Auth Credentials	21.086 s	C8Y-Basic-Auth
Ignore Containers Marked With A Specific Label	28.582 s	Container
Grace period to allow container to startup	5.025 s	Operations
Service is up	0.178 s	Operations
Get Logfile Request	2.501 s	Operations
Get Configuration File	4.983 s	Operations
Set Configuration File	2.669 s	Operations
Execute Shell Command	2.499 s	Operations
Install application using docker compose	28.791 s	Operations
Get Container Logs	4.655 s	Operations
Get Container Logs without explicit container name	4.664 s	Operations
Get Container Logs For Non-existent container	2.503 s	Operations
Update From Legacy Versions	144.330 s	Self-Update-Compat
Trigger self update via local command	24.932 s	Self-Update
Self update should only update if there is a new image	21.178 s	Self-Update
Self update using software update operation	105.655 s	Self-Update
Rollback when trying to install a non-tedge based image	24.378 s	Self-Update
Self update using software update operation using Container type	118.479 s	Self-Update
Cloud Connection is Online	0.555 s	Telemetry
Service status	0.307 s	Telemetry
Sends measurements	2.602 s	Telemetry