Fix: Use Salt Grains for OTEL Collector Config Values

[kapoorabhishek24]

The OTEL Collector config values (url.domain, lit.subnet.id) were being set via sed replacement in
common.sh. This was fragile because Salt could overwrite the file on subsequent runs, resetting the values to placeholders.

Changes

Refactored to use Salt grains for dynamic configuration:

• common.sh: Sets grains during guest creation instead of sed-patching the config file
• otel-collector-config.yaml.j2: New Jinja2 template that reads values from grains
• init.sls: Updated to render the template with Jinja