Add Helm Chart (#454)

helm/opengist/README.md

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+# Opengist Helm Chart
+
+![Version: 0.1.0](https://img.shields.io/badge/Version-0.1.0-informational?style=flat-square) ![AppVersion: 1.10.0](https://img.shields.io/badge/AppVersion-1.10.0-informational?style=flat-square)
+
+Opengist Helm chart for Kubernetes.
+
+* [Install](#install)
+* [Configuration](#configuration)
+* [Dependencies](#dependencies)
+  * [Meilisearch Indexer](#meilisearch-indexer)
+  * [PostgreSQL Database](#postgresql-database)
+
+## Install
+
+```bash
+helm repo add opengist https://helm.opengist.io
+ 
+helm install opengist opengist/opengist
+```
+
+## Configuration
+
+This part explains how to configure the Opengist instance using the Helm chart. The `config.yml` file used by Opengist
+is mounted from a Kubernetes Secret with a key `config.yml` and the values formatted as YAML.
+
+### Using values
+
+Using Helm values, you can define the values from a key name `config`
+
+```yaml
+config:
+  log-level: "warn"
+  log-output: "stdout"
+```
+
+This will create a Kubernetes secret named `opengist` mounted to the pod as a file with the YAML content of the secret,
+used by Opengist.
+
+### Using an existing secret
+
+If you wish to not store sensitive data in your Helm values, you can create a Kubernetes secret with a key `config.yml`
+and values formatted as YAML. You can then reference this secret in the Helm chart with the `configExistingSecret` key.
+
+If defined, this existing secret will be used instead of creating a new one.
+
+```yaml
+configExistingSecret: <name of the secret>
+```
+
+## Dependencies
+
+### Meilisearch Indexer
+
+By default, Opengist uses the `bleve` indexer. **It is NOT available** if there is multiple replicas of the opengist pod (only one pod can open the index at the same time).
+
+Instead, for multiple replicas setups, you **MUST** use the `meilisearch` indexer.
+
+By setting `meilisearch.enabled: true`, the [Meilisearch chart](https://github.com/meilisearch/meilisearch-kubernetes) will be deployed aswell. 
+You must define the `meilisearch.host` (Kubernetes Service) and `meilisearch.key` (value created by Meilisearch) values to connect to the Meilisearch instance in your Opengist config :
+
+```yaml
+index: meilisearch
+index.meili.host: http://opengist-meilisearch:7700 # pointing to the K8S Service
+index.meili.api-key: MASTER_KEY                    # generated by Meilisearch
+```
+
+If you want to use the `bleve` indexer, you need to set the `replicas` to `1`.
+
+### PostgreSQL Database
+
+By default, Opengist uses the `sqlite` database. If needed, this chart also deploys a PostgreSQL instance.
+
+By setting `postgresql.enabled: true`, the [Bitnami PostgreSQL chart](https://github.com/bitnami/charts/tree/main/bitnami/postgresql) will be deployed aswell.
+You must define the `postgresql.host`, `postgresql.port`, `postgresql.database`, `postgresql.username` and `postgresql.password` values to connect to the PostgreSQL instance.
+
+Then define the connection string in your Opengist config:
+
+```yaml
+db-uri: postgres://user:password@opengist-postgresql:5432/opengist
+```
+Note: `opengist-postgresql` is the name of the K8S Service deployed by this chart.