adding a config file for influxdb container.

INFLUXDB_GRAPHITE_TEMPLATES expects multiple templates to be separated by ',' (see influxdata/influxdb#7323),
in the same time ',' is used to separate multiple additional tags for a single template (see https://docs.influxdata.com/influxdb/v1.8/supported_protocols/graphite/#adding-tags)
So unfortunately it's impossible to configure a template with multiple additional tags thru INFLUXDB_GRAPHITE_TEMPLATES env variable,
and providing a config file with templates is the only available option for this.

in order to check the whole influxdb config (including default values) you should start docker-compose setup and attach to the
influxdb container (note that execution of docker compose commands is done in the metrics directory):
    cd metrics
    docker compose up -d
    docker compose exec influxdb bash

then you can run this command in the influxdb container's shell:
    influxd config

the default configuration file for influxdb container is located at '/etc/influxdb/influxdb.conf', you can print its content or check
how the whole configuration looks like with it using these commands:
    cat /etc/influxdb/influxdb.conf
    INFLUXDB_CONFIG_PATH=/etc/influxdb/influxdb.conf influxd config

.gitignore

@@ -18,3 +18,4 @@ _build
 rebar3.crashdump
 *~
 rebar3
+metrics/influxdb_data

metrics/docker-compose.yml

@@ -6,9 +6,16 @@ services:
       - "2003:2003"
     networks:
       - metrics-network
+    volumes:
+      - type: "bind"
+        source: "./influxdb_data"
+        target: "/influxdb"
+      - type: "bind"
+        source: "./influxdb.conf"
+        target: "/influxdb.conf"
+        read_only: true
     environment:
-      INFLUXDB_GRAPHITE_ENABLED: "true"
-      INFLUXDB_GRAPHITE_TEMPLATES: 'instance.measurement*'
+      INFLUXDB_CONFIG_PATH: "/influxdb.conf"
   grafana:
     image: "grafana/grafana:6.7.3"
     ports:

metrics/influxdb.conf

@@ -0,0 +1,10 @@
+[meta]
+  dir = "/influxdb/meta"
+
+[data]
+  dir = "/influxdb/data"
+  wal-dir = "/influxdb/wal"
+
+[[graphite]]
+  enabled = true
+  templates = ["instance.measurement*"]