Support customized junit report format

[InfiniteXyy]

Clear and concise description of the problem

Currently, when using reporters: ["junit"], only testsuites is configurable, could we also make classNameTemplate andtitleTemplate comfigurable, so that I can use custom seperator between classname and title, or remove classname totally.

vitest/packages/vitest/src/node/reporters/junit.ts

Lines 167 to 169 in f91da48

	await this.writeElement('testcase', {
	classname: filename,
	name: task.name,

Suggested solution

In jest-junit there are some configurable env values, like JEST_JUNIT_CLASSNAME

and we also have VITEST_JUNIT_SUITE_NAME in vitest, we could add more env variables to help config the junit output

Alternative

No response

Additional context

The configratuion for jest-junit documentation:
https://github.com/jest-community/jest-junit#configuration

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[AriPerkkio]

Instead of supporting environment variables we should open an API for providing reporter options. The coverage reporters already support this kind of API:

vitest/docs/config/index.md

Lines 786 to 800 in 726a57e

	The reporter has three different types:
	- A single reporter: `{ reporter: 'html' }`
	- Multiple reporters without options: `{ reporter: ['html', 'json'] }`
	- A single or multiple reporters with reporter options:
	<!-- eslint-skip -->
	```ts
	{
	reporter: [
	['lcov', { 'projectRoot': './src' }],
	['json', { 'file': 'coverage.json' }],
	['text']
	]
	}
	```

This is something that 3rd party custom reporters could also utilize.

[InfiniteXyy]

I created a simple PR for my own usecase (to remove the filepath in className), would it be OK for the merge?
#3808