Auto Detect MySQL Version and Use in vtgate mysql_server_version Flag

[mattlord]

Description

We were using the default value for the vtgate --mysql_server_version flag of 5.7.9-vitess even when the tests were using MySQL 8.0. This work auto detects the MySQL version that will be used for the tests and uses that in the vtgate --mysql_server_version flag unless a specific mysql_server_version has been specified for the test. This way we retain the ability to use custom values for this flag when needed, while otherwise defaulting to a reasonable version.

This will allow us to move more tests to MySQL 8.0 in a seamless way over the coming months as 5.7 is slated for EOL in October, 2023.

⚠️ This PR exposed a bug in v14+ that could cause incorrect collation handling and vtgate crashes: #10712. This PR addresses that as well, which is why I added the Backport to: release-14.0 label.

Related Issue(s)

• Related to: Add MySQL 8 Support to Backup Tests #10691
• Fixes: Bug Report: vtgate crashes executing SELECT CAST("test" AS CHAR(60)) #10712

Checklist

• Should this PR be backported?
• Tests were added or are not required
• Documentation was added or is not required

[vitess-bot]

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[GuptaManan100]

Looks good to me! We might have to remove the mysql_server_version being set in some tests that are currently doing it because we now do it in this central place.

[mattlord]

Looks good to me! We might have to remove the mysql_server_version being set in some tests that are currently doing it because we now do it in this central place.

I pushed another commit removing any other place we used a static string in the endtoend tests: c5cf717

If it causes tests failures then I'll either revert that or investigate and fix the failures.

[frouioui]

Looks good to me!

[vmg]

I like this approach, a lot of the engine/planner tests have always been written for 8.0 and porting them to 5.7 right before 5.7 is EOL seems wasteful.