[Blog] Add an In-Depth Analysis of the SeaTunnel Job Submission Flow

[nzw921rx]

Purpose of this pull request

This PR adds a bilingual blog article explaining the complete SeaTunnel job submission and scheduling flow.

• English version: blog/2026-08-08-seatunnel-submit-job-flow.md
• Chinese version: i18n/zh-CN/docusaurus-plugin-content-blog/2026-08-08-seatunnel-submit-job-flow.md

The article follows the main execution path:

SubmitJobServlet
  -> JobInfoService
  -> MasterNode / CoordinatorService
  -> JobMaster
  -> PhysicalPlan
  -> SubPlan
  -> PhysicalVertex
  -> TaskExecutionService

It explains:

• Master detection and request forwarding
• CoordinatorService and JobMaster initialization
• Logical DAG to PhysicalPlan conversion
• Pipeline resource allocation and state transitions
• Local and remote TaskGroup deployment
• Failure, cancellation, and recovery branches

[nzw921rx]

@davidzollo can you help me review this PR? thank you very much🚀