Migrate kafka-user Module to redpanda-user

Migrate every usage of the internal `kafka-user` Terraform module to the new
`redpanda-user` module.

For each Terraform repository:
1. Find every `module "<name>" { ... }` block whose `source` references
   `kafka-user` (e.g.,
   `git::ssh://[email protected]/example/terraform-modules.git//kafka-user?ref=...`).
2. Rewrite the `source` to point at the `redpanda-user` module at the pinned target
   version (e.g., `//redpanda-user?ref=v1.0.0`, pass the version explicitly).
3. Rename input arguments using the input map:
   - `username` → `principal`
   - `kafka_cluster_id` → `redpanda_cluster_id`
   - `topic_acls = { topic = ["WRITE"] }` keeps the same shape but values must use
     the Redpanda ACL operation names (`READ`, `WRITE`, `DESCRIBE`, `ALL`)
4. Update downstream references to module outputs across the same repo:
   - `module.x.kafka_password` → `module.x.sasl_password`
   - `module.x.kafka_username` → `module.x.principal`
5. If a call site uses an input not in the rename map, leave it untouched,
   prepend `[MANUAL-REVIEW]` to the PR title, and list the unmapped inputs
   under a `## Inputs needing manual review` section in the PR body.
6. Do not run `terraform apply`, the change must be reviewed by service owners.

The Problem

Once the platform team publishes the `redpanda-user` Terraform module, every service that previously instantiated `kafka-user` needs to switch; otherwise both modules race to own the same SASL principals and topic ACLs.

The signatures differ slightly (`username` → `principal`, `topic_acls` shape changes), so the swap can’t be a pure find-and-replace. Each call site needs the input mapping applied carefully.

What Tidra Does

1. Finds every module "..." block whose source points at the kafka-user module
2. Rewrites source to the redpanda-user module at the version you specify
3. Translates input arguments using the documented input map (username → principal, etc.)
4. Updates downstream references to module outputs (module.x.kafka_password → module.x.sasl_password)
5. Opens one PR per repo and lists any call sites with unmappable inputs for human review

Before & After

Customization Tips

• Input map: Provide the full input rename map. Anything not mapped is left to a human review with a [MANUAL-REVIEW] title prefix on the PR.
• Output references: List the output renames (old name → new name) so downstream references update consistently.
• Module version: Pin the target redpanda-user version explicitly so the migration is reproducible.