Add support for environment-specific field values

Problem/Motivation

Currently, the module supports a single "lower environment" value that applies to all non-production environments (dev, stage, test, etc.). However,
different environments may need different values.

For example:

• Staging might need to point to https://api-staging.example.com
• Development might need to point to https://api-dev.example.com
• Local might need to point to http://localhost:8000

Users currently have to maintain separate trackers or manually update values when syncing to different environments, which is error-prone and
time-consuming.

Steps to reproduce

1. Create a field value tracker with a lower environment value
2. Sync database to staging environment and run drush fvt:update
3. Sync database to dev environment and run drush fvt:update
4. Notice both environments receive the same value, when they may need different values

Proposed resolution

Add support for environment-specific values while maintaining backward compatibility:

1. Configurable environments - Add simple YAML config (field_value_tracker.environments.yml) listing available environments
   with labels and descriptions
2. Environment-specific values field - Add environment_values map field to store per-environment values
3. Enhanced Drush command - Add --env flag to specify which environment to use:
   

   drush fvt:update --env=stage
     drush fvt:update --env=dev
     drush fvt:update  # Uses default "all" value

4. Smart fallback logic - If no environment-specific value exists for the specified environment, fall back to the default
   lower_env_value
5. Backward compatibility - Existing trackers continue to work unchanged; lower_env_value becomes the "all environments"
   default
6. Update hook - Provide update hook to install new configuration and add new field

Remaining tasks

• ✅ Create config schema for environments
• ✅ Create default environments config YAML
• ✅ Add environment_values field to entity
• ✅ Update form with environment-specific value fields using proper DI
• ✅ Add --env flag to Drush command
• ✅ Update Drush command logic for environment-specific values
• ✅ Create update hook for migration
• ✅ Add comprehensive tests
• ⬜ Code review
• ⬜ Manual testing on real environments
• ⬜ Update documentation (README)

User interface changes

The tracker edit form at /admin/config/development/field-value-tracker/{id}/edit will show:

• Lower Environment Value - Relabeled as "All Environments (Default)" with description explaining it's used as the fallback
• Environment-specific Values - New collapsible details section containing:
  • Dynamic textarea fields for each configured environment (stage, dev, etc.)
  • Each field labeled with the environment's human-readable label
  • Optional - leave empty to use the default "all" value

Screenshot: (Will be added after manual testing)

API changes

New field on field_value_tracker entity:

• environment_values - Map field storing environment ID => value pairs

Updated Drush command:

• field-value-tracker:update (alias: fvt:update)
  • New option: --env=ENVIRONMENT - Specify target environment
  • Backward compatible - running without --env uses default value

New configuration:

• field_value_tracker.environments - Simple config listing available environments

Data model changes

field_value_tracker entity:

• New field: environment_values
  • Type: map
  • Required: No
  • Stores: Array of environment_id => value mappings
• Existing field: lower_env_value
  • Behavior change: Now serves as "all environments" default
  • Still required
  • Backward compatible

New configuration object:

• field_value_tracker.environments.yml
  • Structure: Keyed array of environment definitions
  • Each environment has: label and description
  • Ships with: all, stage, dev
  • User-customizable via config management

Update hook:

• field_value_tracker_update_11001() - Installs new config and adds environment_values field to existing entities