docs: rfc on possible config parameter change process

docs/rfc/rfc-008-parameter-and-secrets-config-change-process.md

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+# RFC: Parameter and Secret Management Changes
+
+## Background
+
+Our Laminas app uses AWS Parameter Store and Secrets Manager for configuration management. We've experienced runtime failures during releases etc when parameter placeholders don't exist in AWS. This creates a need for a defined process to manage parameter and secret changes in vol-app.
+
+## Proposed Solution
+
+### Process for Parameter Store Management
+
+When adding or modifying parameters in Laminas config files:
+
+1. Developer identifies need for new parameter
+2. Developer MUST:
+    - Create a branch in `vol-terraform` repository
+    - Determine if the parameter will be the same across multiple environments or change individually per environment  
+    - Add parameter values to appropriate files in `/etc/` - group for common, environment ones for individual 
+3. Developer MUST create two linked PRs:
+    - `vol-terraform` PR with parameter additions
+    - `vol-app` PR with application changes to config
+4. Both PRs MUST reference each other in their descriptions
+5. The `vol-terraform` PR should be merged before or at the same time as the application PR
+
+## Notes
+
+The vol-terraform etc folder contains the files that define parameters. There are two group files which contain values shared by all environments in an account, then per-environment files for environment-specific values. Please use the least-specific file possible for your changes.
+
+## File Structure Example
+
+```
+/etc/
+├── env_eu-west-1_dev.tfvars     # Dev-specific values
+├── env_eu-west-1_pp.tfvars      # PP-specific values
+├── group_nonprod.tfvars         # Shared non-prod values
+└── group_prod.tfvars            # Shared prod values
+```
+
+### Process for Secret Management
+
+As we should not store secret values in a repository, AWS Secrets Manager is used. If a developer needs a new secret it is proposed that they:
+
+1. Raises a ticket for Infrastructure team, linked to the ticket they are working on with:
+    - Secret placeholder name
+    - Description of purpose
+    - Required environments
+    - Where the value can be found / who is responsible for updating it in future etc
+2. Infrastructure team will:
+    - Create the secret in AWS Secrets Manager
+    - Notify the developer upon completion
+3. Developer can then merge their application changes