add configs api docs

docs/configs-api.md

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+# Configs API
+
+The configs service provides an API-driven multi-tenant approach to handling various configuration files for prometheus. The service hosts an API where users can read and write Prometheus rule files, Alertmanager configuration files, and Alertmanager templates to a database.
+
+Each tenant will have it's own set of rule files, Alertmanager config, and templates. A POST operation will effectively replace the existing copy with the configs provided in the request body.
+
+## Configs Format
+
+At the current time of writing, the API is part-way through a migration from a single Configs service that handled all three sets of data to a split API ([Tracking issue](https://github.com/cortexproject/cortex/issues/619)). All APIs take and return all sets of data.
+
+The following schema is used both when retrieving the current configs from the API and when setting new configs via the API.
+
+### Schema:
+
+```json
+{
+    "id": 99,
+    "rule_format_version": "2",
+    "config": {
+        "alertmanager_config": "<standard alertmanager.yaml config>",
+        "rules_files": { 
+            "rules.yaml": "<standard rules.yaml config>",
+            "rules2.yaml": "<standard rules.yaml config>"
+         },
+        "template_files": {
+            "templates.tmpl": "<standard template file>",
+            "templates2.tmpl": "<standard template file>"
+        }
+    }
+}
+```
+
+### Formatting
+
+`id` - should be incremented every time data is updated; Cortex will use the config with the highest number.
+
+`rule_format_version` - allows compatibility for tenants with config in Prometheus V1 format. Pass "1" or "2" according to which Prometheus version you want to match.
+
+`config.alertmanager_config` - The contents of the alertmanager config file should be as described [here](https://prometheus.io/docs/prometheus/latest/configuration/alerting_rules/), encoded as a single string to fit within the overall JSON payload.
+
+`config.rules_files` - The contents of a rules file should be as described [here](http://prometheus.io/docs/prometheus/latest/configuration/recording_rules/), encoded as a single string to fit within the overall JSON payload.
+
+`config.template_files` - The contents of a template file should be as described [here](https://prometheus.io/docs/alerting/notification_examples/#defining-reusable-templates), encoded as a single string to fit within the overall JSON payload.
+
+## Endpoints
+
+### Manage Alertmanager
+
+`GET /api/prom/configs/alertmanager` - Get current Alertmanager config
+
+- Normal Response Codes: OK(200)
+- Error Response Codes: Unauthorized(401), NotFound(404)
+
+`POST /api/prom/configs/alertmanager` - Replace current Alertmanager config
+
+- Normal Response Codes: NoContent(204)
+- Error Response Codes: Unauthorized(401), BadRequest(400)
+
+`POST /api/prom/configs/alertmanager/validate` - Validate Alertmanager config
+
+Normal Response: OK(200)
+```json
+{ 
+    "status": "success"
+}
+```
+
+Error Response: BadRequest(400)
+```json
+{ 
+    "status": "error",
+    "error": "error message"
+}
+```
+
+### Manage Rules
+
+`GET /api/prom/configs/rules` - Get current rule files
+
+- Normal Response Codes: OK(200)
+- Error Response Codes: Unauthorized(400), NotFound(404)
+
+`POST /api/prom/configs/rules` - Replace current rule files
+
+- Normal Response Codes: NoContent(204)
+- Error Response Codes: Unauthorized(401), BadRequest(400)
+
+### Manage Templates
+
+`GET /api/prom/configs/templates` - Get current templates
+
+- Normal Response Codes: OK(200)
+- Error Response Codes: Unauthorized(401), NotFound(404)
+
+`POST /api/prom/configs/templates` - Replace current templates
+
+- Normal Response Codes: NoContent(204)
+- Error Response Codes: Unauthorized(401), BadRequest(400)
+
+### Deactivate/Restore Configs
+
+`DELETE /api/prom/configs/deactivate` - Disable configs for a tenant
+
+- Normal Response Codes: OK(200)
+- Error Response Codes: Unauthorized(401), NotFound(404)
+
+`POST /api/prom/configs/restore` - Re-enable configs for a tenant
+
+- Normal Response Codes OK(200)
+- Error Response Codes: Unauthorized(401), NotFound(404)
+
+These API endpoints will disable/enable the current Rule and Alertmanager configuration for a tenant.
+
+Note that setting a new config will effectively "re-enable" the Rules and Alertmanager configuration for a tenant.