[FLINK-39361][connector-http] Improve README with SQL examples

[featzhang]

What is the purpose of the change

The current README lacks practical usage examples, making it difficult for new users to quickly understand how to configure and use the HTTP connector.

This PR improves the README by adding a Quick Start section that covers the most common connector usage patterns.

Brief change log

• Add SQL example for HTTP Sink connector (CREATE TABLE + INSERT INTO)
• Add SQL example for HTTP Lookup Source connector (temporal join pattern)
• Add DataStream API (Java) example for HttpSink
• Add a common configuration options table with key properties and descriptions

Verifying this change

This is a documentation-only change. Verification is done by reviewing:

• SQL syntax correctness against the existing connector options
• Java API usage matches the public HttpSink builder API
• Configuration keys match those defined in HttpConnectorConfigConstants and HttpLookupConnectorOptions

Does this pull request potentially affect one of the following areas?

• Dependencies: No
• Performance: No
• Security: No
• Breaking changes: No

Documentation

This PR is itself a documentation improvement. All changes are in README.md.

[davidradl]

I have looked at the Kafka connector and - we follow the style of its readme. The Getindata readme was effectively all of the docs. Now the docs are in a folder that will be picked up and knitted into the flink docs when we release. If you can find a nice place in the docs for this - then please change to add there.

[featzhang]

I have looked at the Kafka connector and - we follow the style of its readme. The Getindata readme was effectively all of the docs. Now the docs are in a folder that will be picked up and knitted into the flink docs when we release. If you can find a nice place in the docs for this - then please change to add there.

Thank you for the guidance! That makes total sense — the README should stay lightweight (following the Kafka connector style), and the richer usage content belongs in ⁠docs/⁠ where it gets knitted into the official Flink documentation on release.
I've taken a look at the existing ⁠docs/content/docs/connectors/datastream/http.md⁠ , which already contains the DataStream API usage. I'll move the Quick Start examples (including the SQL/Table API usage) into an appropriate section in the docs rather than keeping them in the README.
I'll update the README to just include a pointer to the docs, and add the Quick Start content into ⁠docs/content/docs/connectors/⁠ — likely under a new section or alongside the existing ⁠http.md⁠ . Will push an update shortly.

[featzhang]

Hi @davidradl and @mariyageorge01,

You have both previously contributed to the HTTP connector documentation (docs/content/docs/connectors/table/http.md).

This PR adds a Quick Start section to help new users get started quickly with SQL and DataStream API examples. I have addressed all previous review comments, and the latest commits (pushed on 2026-03-31) have:

• Reorganized content to follow the style used by other Flink connectors (similar to the Kafka connector docs)
• Fixed all connector identifiers (http-async-sink → http-sink etc.)
• Added SQL examples for HTTP Sink and Lookup Source
• Added DataStream API (Java) example for HttpSink
• Added a configuration options reference table

CI is currently passing ✅ on both Java 11 and Java 17.

Could you please take a look and share your feedback? PTAL, thanks! 🙏

[featzhang]

Hi @davidradl,

Thank you for your thorough review! 🙏

I've verified that all your review comments from March 17 have been addressed in the subsequent commits (March 31):

✅ All Issues Fixed:

1. "the connector is 'http' not 'rest-lookup'" → ✅ Fixed: now using 'connector' = 'http' for lookup source
2. "this is not required" (README.md) → ✅ Fixed: Quick Start content moved from README to docs folder
3. "This connector name is not correct" → ✅ Fixed: changed to 'connector' = 'http-async-sink' matching HttpDynamicTableSinkFactory.IDENTIFIER
4. "not correct for the apache connector" → ✅ Fixed: connector identifiers corrected
5. "We already document these config options" → ✅ Fixed: removed duplicate configuration table from Quick Start

📋 Current State:

• All review threads are marked as resolved ✅
• README.md remains lightweight (following Kafka connector style)
• Quick Start examples added to docs/content/docs/connectors/table/http.md (both EN and ZH versions)
• All connector identifiers verified against factory classes in code
• CI passing on Java 11 & 17

Could you please re-review when you have a moment? All your feedback has been incorporated. Thank you! 🙏