Add ScalarDB Cluster test with MySQL

[yito88]

Description

Add a test with MySQL

Related issues and/or PRs

Depends on #169

Changes made

• Setup MySQL in ScalarDB Cluster test

Checklist

The following is a best-effort checklist. If any items in this checklist are not applicable to this PR or are dependent on other, unmerged PRs, please still mark the checkboxes after you have read and understood each item.

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• Any remaining open issues linked to this PR are documented and up-to-date (Jira, GitHub, etc.).
• Tests (unit, integration, etc.) have been added for the changes.
• My changes generate no new warnings.
• Any dependent changes in other PRs have been merged and published.

Additional notes (optional)

Provide any additional information or notes that may be relevant to the reviewers or stakeholders.

[Copilot]

Pull request overview

This PR adds MySQL support as a storage backend for ScalarDB Cluster tests. The implementation refactors how database types are handled, moving from a :cluster database option to using storage backends (postgres/mysql) with an environment variable flag to enable cluster mode.

Key changes:

• Added MySQL as a supported storage backend alongside PostgreSQL for ScalarDB Cluster tests
• Refactored database configuration to use environment variables for Docker credentials and cluster mode detection
• Updated GitHub Actions workflows to use the new configuration approach with storage backend selection

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
scalardb/src/scalardb/runner.clj	Renamed db-keys to supported-dbs, added :mysql support, refactored gen-db to route based on :cluster? env var instead of db type, removed docker credential CLI options
scalardb/src/scalardb/db_extend.clj	Removed get-db-type method from DbExtension protocol
scalardb/src/scalardb/db/postgres.clj	Removed get-db-type implementation, updated gen-db signature to accept variadic args
scalardb/src/scalardb/db/cluster.clj	Added MySQL database setup, refactored configuration to use environment variables for Docker credentials, added database-specific connection properties
scalardb/src/scalardb/db/cassandra.clj	Updated gen-db signature to accept variadic args
scalardb/project.clj	Added :cluster? environment variable flag
README.md	Updated documentation to reflect new environment variable approach for Docker credentials
.github/workflows/test.yml	Updated to use environment variables and --db postgres instead of --db cluster
.github/workflows/daily.yml	Updated to use environment variables and --db postgres instead of --db cluster
.github/workflows/cluster-test.yml	Added storage backend selection input, changed Java version to 21, updated to use environment variables

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[feeblefakie]

Overall, looking good. Left one comment. PTAL!

[feeblefakie]

LGTM! Thank you!
Left one question for clarification.

[brfrn169]

LGTM! Thank you!