Add support for selective test run with a testplan

[delatrie]

There is a general mechanism used by Allure integrations to run tests selectively. It uses a testplan - a .json file with the following schema:

{
    "type": "object",
    "properties": {
        "tests": {
            "type": "array",
            "items": {
                "type": "object",
                "properties": {
                    "id": { "type": "string" },
                    "selector": { "type": "string" }
                }
            }
        }
    }
}

A path to a testplan is provided as a value of the ALLURE_TESTPLAN_PATH environment variable.

If a valid testplan file is provided, only matched tests should be run. A test is matched if there is at least one entry in the tests array, such that:

1. It has either the id property, or the selector property or both, AND
2. If the id property is present in the entry, it must be the same as the Allure ID of the test, AND
3. If the selector property is present in the entry, it must be the same as the fullName of the test.

Motivation

Put allure-csharp integrations in line with other Allure integrations in terms of features.

[delatrie]

Done. Included in 2.10.0