Implement H2-first CI strategy with workflow dependencies

[Copilot]

Restructure CI/CD to run H2 tests as a fast quality gate before expensive multi-database tests. Saves cycles by catching fundamental issues early without spinning up containers.

Changes

New test flag: enableH2Tests

• Added system property (default: true) to 13 test files
• Follows existing pattern (enablePostgresTests, enableMySQLTests, etc.)
• Uses consistent URL matching: url.toLowerCase().contains("h2:")

@BeforeAll
public static void setup() {
    isH2TestEnabled = Boolean.parseBoolean(System.getProperty("enableH2Tests", "true"));
    // ...
}

Main CI: H2-only execution

• Updated test command: -DenableH2Tests=true -DenablePostgresTests=false -DenableMySQLTests=false
• Runs in-memory H2 tests across Java 11/17/21/22
• ~5-10 min feedback loop vs. full suite

Database workflows: Gated on Main CI success

• Added workflow_run trigger to 8 database-specific workflows (MySQL, Postgres, MariaDB, Oracle, SQL Server, DB2, CockroachDB, Multinode)
• On push to main: only execute if Main CI succeeds
• On pull requests: run independently for validation
• Manual triggering via workflow_dispatch still available

on:
  workflow_run:
    workflows: ["Main CI"]
    types: [completed]
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  mysql-tests:
    if: ${{ github.event_name == 'pull_request' || (github.event_name == 'workflow_run' && github.event.workflow_run.conclusion == 'success') }}

Documentation

• Created documents/ci-cd-workflow-structure.md explaining workflow execution order and rationale
• Updated documents/code-contributions/setup_and_testing_ojp_source.md with new flag
• Added CI/CD docs link to main README

Impact

H2 catches compilation errors, JDBC contract violations, and major bugs before TestContainers spin up. Database tests run in parallel only when base functionality is confirmed working.

Original prompt

I want the workflows to run in a different order, first only the Main CI should run and in the main CI only H2 database related tests should run, to do that create a new flag enableH2Tests in the same fashion as existing enablePostgresTests or enableMySQLTests etc, then only enable H2 test in the main CI workflow.
All other workflows should only execute if the Main CI succeeds.
Add documentation or update existing if possible explaining the new way and the reason which is to save cycles as per the H2 tests are cheaper and work as a fail fast mechanism in which if something majorly wrong happen it already fails without having to run the full suite of tests.

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[rrobetti]

Something is wrong with this PR, too many changes showing up in the diff.