[feature:gsoc26] Add Docker support for InfluxDB 2.0 and Elasticsearch backends

Currently docker-openwisp only ships with InfluxDB 1.8. This issue tracks adding Docker Compose entries and environment variable mappings for both InfluxDB 2.0 and Elasticsearch.

Scope

• Add Docker Compose service support for InfluxDB 2.0.
• Add Docker Compose service support for Elasticsearch.
• Add environment variable mappings required by OpenWISP Monitoring for the new backends.
• Allow operators to switch among InfluxDB 1.8, InfluxDB 2.0, and Elasticsearch via a documented environment variable or set of variables.
• Provide sane defaults for local development and basic deployments.
• Allow advanced configuration through environment variables.
• Include persistent volumes for the new services where appropriate.
• Document any upgrade or migration notes needed when introducing the new services.

InfluxDB 2.0 environment mappings to cover

• URL or host/port configuration.
• Organization.
• Token.
• Bucket name.
• Retention configuration if exposed.

Elasticsearch environment mappings to cover

• Hosts.
• Scheme.
• Authentication or API key options.
• Index name.
• Index Lifecycle Management policy options if exposed.
• Shard and replica settings if exposed.
• Resource settings if needed for reliable local development.

Acceptance criteria

• Docker-based deployments can run with InfluxDB 2.0 without manual installation steps.
• Docker-based deployments can run with Elasticsearch without manual installation steps.
• Operators can switch among InfluxDB 1.8, InfluxDB 2.0, and Elasticsearch through documented environment variables.
• Default values are sufficient for a basic working setup.
• Advanced values can be overridden without editing application code.