docs: add InfluxDB Sink connector page (depends on upstream README)

[mlevkov]

Context

apache/iggy/core/connectors/sinks/influxdb_sink/ ships in the Iggy connector runtime but is not represented on the docs site:

• Not listed in the Available Connectors table.
• No per-connector page under /docs/connectors/sinks/ analogous to the existing pages for Elasticsearch, Postgres, MongoDB, Quickwit, Iceberg, or Stdout.

Discovered alongside the Generic HTTP Sink docs effort tracked in #39.

Dependency

Unlike the HTTP sink (which has a comprehensive upstream README at http_sink/README.md), the InfluxDB sink directory currently contains no README.md — only Cargo.toml, config.toml, and src/. There is no canonical source content to curate from.

Two paths to unblock:

1. Upstream README first: open a companion issue/PR on apache/iggy to add core/connectors/sinks/influxdb_sink/README.md covering configuration, line-protocol semantics, and InfluxDB v2 auth. Then mirror to the site following the curation pattern already established for other sinks.
2. Reverse-engineer: derive a minimal site page from the example config.toml and source code. Faster, but bypasses the source-of-truth model used elsewhere.

Path (1) is preferred — it keeps apache/iggy as the canonical reference and avoids drift.

Configuration Surface (from config.toml)

For scoping reference only — full options should come from the eventual upstream README:

Key	Purpose
url	InfluxDB v2 endpoint (default example: http://localhost:8086)
org, bucket, token	InfluxDB v2 auth + tenancy
measurement	Line-protocol measurement name
precision	Timestamp precision (e.g. ns)
batch_size	Write batch size
payload_format	Payload encoding (e.g. json)
include_metadata, include_checksum, include_origin_timestamp	Envelope toggles (matches Postgres/HTTP sink convention)
include_stream_tag, include_topic_tag, include_partition_tag	Tag injection for routing in InfluxDB queries
max_retries, retry_delay, timeout	Retry/timeout semantics

Proposed Changes (Once Upstream README Exists)

Same 3-file pattern as #39:

1. Add content/docs/connectors/sinks/influxdb.mdx — sourced from the future upstream README, curated to match sibling sink page style.
2. Edit content/docs/connectors/sinks/meta.json — insert "influxdb" in the pages array.
3. Edit content/docs/connectors/introduction.mdx — add InfluxDB to the Sink row of the Available Connectors table.

Naming & Style (Proposed, mirroring #39)

Surface	Value
File / URL slug	influxdb.mdx → /docs/connectors/sinks/influxdb
Page title (frontmatter)	InfluxDB Sink
Available Connectors table cell	InfluxDB

References

• Companion HTTP Sink docs effort: docs: add Generic HTTP Sink connector page and update connectors table #39
• Upstream connector source: core/connectors/sinks/influxdb_sink