docs: restructure database update endpoints documentation

[dosubot]

Update documentation for #4013

Reorganized the Database Service Update Endpoints section for improved clarity and usability. The documentation now clearly outlines that all five database services (PostgreSQL, MySQL, MariaDB, MongoDB, Redis) share a common update interface with the dockerImage parameter, providing users with better guidance on custom Docker image configuration and version pinning options.

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Greptile Summary

This PR adds extensive API documentation to apps/api/README.md, covering environment variables, API endpoints (jobs, search, database updates), and whitelabeling endpoints. While the PR title says "restructure database update endpoints documentation," the actual scope is much broader — it's effectively a full API reference for the apps/api service.

• The dockerImage parameter documentation for database update endpoints is accurate and matches the schemas in packages/server/src/db/schema/
• Environment variable naming error: DOCKER_API_VERSION in the docs should be DOKPLOY_DOCKER_API_VERSION to match the implementation in packages/server/src/constants/index.ts
• Documented-but-unimplemented env vars: INNGEST_EVENTS_RECEIVED_AFTER and INNGEST_JOBS_MAX_EVENTS are documented as configurable but are not actually used in the service code; the max events value is hardcoded to 500 (not 100 as documented)
• Missing newline at end of file

Confidence Score: 3/5

• Documentation-only PR with no runtime impact, but contains inaccuracies that could mislead users.
• Score of 3 reflects that while this is a docs-only change with zero runtime risk, it contains a concrete factual error (wrong env var name) and documents features that don't actually exist in the implementation, which could confuse users.
• apps/api/README.md — environment variable names and defaults should be verified against the actual implementation before merging.

_{Last reviewed commit: d287e2a}

Greptile also left 2 inline comments on this PR.

[greptile-apps]

Incorrect environment variable name

The documented variable name DOCKER_API_VERSION does not match the actual implementation. In packages/server/src/constants/index.ts, the variable is DOKPLOY_DOCKER_API_VERSION:

export const DOKPLOY_DOCKER_API_VERSION =
	process.env.DOKPLOY_DOCKER_API_VERSION;

Users following this documentation would set the wrong environment variable and it would have no effect.

Suggested change

	- **DOCKER_API_VERSION** (optional) - Specifies which Docker API version to use when connecting to the Docker daemon. If not set, the Docker client uses the default API version.
	- **DOKPLOY_DOCKER_API_VERSION** (optional) - Specifies which Docker API version to use when connecting to the Docker daemon. If not set, the Docker client uses the default API version.

[greptile-apps]

Documented env vars not implemented in code

INNGEST_EVENTS_RECEIVED_AFTER and INNGEST_JOBS_MAX_EVENTS are documented as functional environment variables, but they are not actually read or used in apps/api/src/service.ts. The implementation hardcodes DEFAULT_MAX_EVENTS = 500 and never references either of these env vars.

Additionally, the documented default for INNGEST_JOBS_MAX_EVENTS ("Default is 100") contradicts the hardcoded value of 500 in the code.

This could confuse users who try to configure these variables expecting them to have an effect. Consider either implementing support for these variables or removing them from the documentation.