Add KV store providers (dynamic configuration only)

Co-authored-by: Jean-Baptiste Doumenjou <jb.doumenjou@gmail.com>

docs/content/providers/zookeeper.md

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+# Traefik & ZooKeeper
+
+A Story of KV store & Containers
+{: .subtitle }
+
+Store your configuration in ZooKeeper and let Traefik do the rest!
+
+## Routing Configuration
+
+See the dedicated section in [routing](../routing/providers/kv.md).
+
+## Provider Configuration
+
+### `endpoints`
+
+_Required, Default="127.0.0.1:2181"_
+
+Defines how to access to ZooKeeper.
+
+```toml tab="File (TOML)"
+[providers.zooKeeper]
+  endpoints = ["127.0.0.1:2181"]
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    endpoints:
+      - "127.0.0.1:2181"
+```
+
+```bash tab="CLI"
+--providers.zookeeper.endpoints=127.0.0.1:2181
+```
+
+### `rootKey`
+
+Defines the root key of the configuration.
+
+_Required, Default="traefik"_
+
+```toml tab="File (TOML)"
+[providers.zooKeeper]
+  rootKey = "traefik"
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    rootKey: "traefik"
+```
+
+```bash tab="CLI"
+--providers.zookeeper.rootkey=traefik
+```
+
+### `username`
+
+Defines a username to connect with ZooKeeper.
+
+_Optional, Default=""_
+
+```toml tab="File (TOML)"
+[providers.zooKeeper]
+  # ...
+  username = "foo"
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    # ...
+    usename: "foo"
+```
+
+```bash tab="CLI"
+--providers.zookeeper.username=foo
+```
+
+### `password`
+
+_Optional, Default=""_
+
+Defines a password to connect with ZooKeeper.
+
+```toml tab="File (TOML)"
+[providers.zooKeeper]
+  # ...
+  password = "bar"
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    # ...
+    password: "bar"
+```
+
+```bash tab="CLI"
+--providers.zookeeper.password=foo
+```
+
+### `tls`
+
+_Optional_
+
+#### `tls.ca`
+
+Certificate Authority used for the secured connection to ZooKeeper.
+
+```toml tab="File (TOML)"
+[providers.zooKeeper.tls]
+  ca = "path/to/ca.crt"
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    tls:
+      ca: path/to/ca.crt
+```
+
+```bash tab="CLI"
+--providers.zookeeper.tls.ca=path/to/ca.crt
+```
+
+#### `tls.caOptional`
+
+Policy followed for the secured connection with TLS Client Authentication to ZooKeeper.
+Requires `tls.ca` to be defined.
+
+- `true`: VerifyClientCertIfGiven
+- `false`: RequireAndVerifyClientCert
+- if `tls.ca` is undefined NoClientCert
+
+```toml tab="File (TOML)"
+[providers.zooKeeper.tls]
+  caOptional = true
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    tls:
+      caOptional: true
+```
+
+```bash tab="CLI"
+--providers.zookeeper.tls.caOptional=true
+```
+
+#### `tls.cert`
+
+Public certificate used for the secured connection to ZooKeeper.
+
+```toml tab="File (TOML)"
+[providers.zooKeeper.tls]
+  cert = "path/to/foo.cert"
+  key = "path/to/foo.key"
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    tls:
+      cert: path/to/foo.cert
+      key: path/to/foo.key
+```
+
+```bash tab="CLI"
+--providers.zookeeper.tls.cert=path/to/foo.cert
+--providers.zookeeper.tls.key=path/to/foo.key
+```
+
+#### `tls.key`
+
+Private certificate used for the secured connection to ZooKeeper.
+
+```toml tab="File (TOML)"
+[providers.zooKeeper.tls]
+  cert = "path/to/foo.cert"
+  key = "path/to/foo.key"
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    tls:
+      cert: path/to/foo.cert
+      key: path/to/foo.key
+```
+
+```bash tab="CLI"
+--providers.zookeeper.tls.cert=path/to/foo.cert
+--providers.zookeeper.tls.key=path/to/foo.key
+```
+
+#### `tls.insecureSkipVerify`
+
+If `insecureSkipVerify` is `true`, TLS for the connection to ZooKeeper accepts any certificate presented by the server and any host name in that certificate.
+
+```toml tab="File (TOML)"
+[providers.zooKeeper.tls]
+  insecureSkipVerify = true
+```
+
+```yaml tab="File (YAML)"
+providers:
+  zooKeeper:
+    tls:
+      insecureSkipVerify: true
+```
+
+```bash tab="CLI"
+--providers.zookeeper.tls.insecureSkipVerify=true
+```