docs(redirector): adds installation documentation

docs/admin/redirector/install.rst

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+============
+Installation
+============
+
+The application is intended to be deployed in AWS using the
+`bc-redirector <https://registry.terraform.io/modules/sr2c/bc-redirector/aws/latest>`_
+Terraform module.
+This deployment is not managed through the portal itself but may be managed alongside the
+IaC that manages the deployment of the portal itself.
+
+Deployment
+----------
+
+The Terraform module takes care of setting up multiple entry-points to the redirector allowing for
+per-pool redirector domains, and also generating the necessary configuration file for the redirector.
+Once deployed, the redirector will not require further manual configuration, although the deployed
+EC2 instance will be accessible via AWS Systems Manager Session Manager if required for debugging.
+
+The following Terraform configuration shows an example using the module:
+
+.. code-block::
+
+   module "redirector" {
+     providers = {
+       aws     = aws,
+       aws.acm = aws.acm
+     }
+     source                    = "sr2c/bc-redirector/aws"
+     # TODO: version           = "x.x.x"
+     namespace                 = "eg"
+     name                      = "redirector"
+     default_redirector_domain = "example.com"
+
+     entry_points = [
+       "example.com",
+       "example.org"
+     ]
+
+     public_key   = var.public_key
+     secret_key   = random_password.secret_key.result
+     update_key   = var.update_key
+
+     maxmind_account_id   = var.maxmind_account_id
+     maxmind_licence_key  = var.maxmind_licence_key
+   }
+
+The `public_key` must match the API key of the public pool configured within the portal.
+The `update_key` may must match the "filename" configured for the distribution list below.
+
+The MaxMind account used will need to have at least a subscription for the GeoIP2 Country
+database.
+A subscription for GeoIP2 City will include the GeoIP2 Country database.
+
+Data Updates
+------------
+
+Once deployed, the redirector must learn about the available mirror resources.
+This requires configuring a :doc:`distribution list <../../user/lists>` inside the portal.
+
+* **Resource Pool**: any (ignored)
+* **Provider**: HTTP POST
+* **Distribution Method**: Redirector Data
+* **Encoding**: JSON (Plain)
+* **Description**: <*description of the redirector instance*>
+* **Container**: \https://<*redirector domain*>/updt
+* **Git Branch/Region**: na
+* **Role ARN**: <*blank*>
+* **Filename**: <*update key*>