Test/add custom analyzer old versions

[drempapis]

Create tests to cover archive-indices and searchable-snapshots created for versions v5/v6 containing a custom analyzer with standard-token-filter.

The test case

1. Creates an index with a custom-analyzer in v5/v6
2. Creates a snapshot of the index
3. Restores the snapshot in version current-1 (currently 8)
4. Upgrades the cluster to version current (currently 9)
5. Verifies compatibility of the index.

The code in review #118154, fails to pass the test

[elasticsearchmachine]

Pinging @elastic/es-search-foundations (Team:Search Foundations)

[benwtrent]

I like the clarity of the tests. I think the enum is a bit too much and we should simply use static final strings for the names.

[benwtrent]

Suggested change

	public enum Snapshot {
	/**
	* Snapshot zip file names for archive and searchable snapshot tests
	*/
	public final class TestSnapshotCases {
	//Index created in vES_5 - Basic mapping
	public static final String ES_VERSION_5 = "5";
	// Index created in vES_5 - Custom-Analyzer - standard token filter
	public static final String ES_VERSION_5_STANDARD_TOKEN_FILTER = "5_custom_analyzer"
	...
	}

Let's make this a simple static class with some static string members. The descriptions are not anything more than what we could provide with a simple java comment.