Data-containing data tiers roles are not mapped onto DATA legacy role

[DaveCTurner]

Elasticsearch version (bin/elasticsearch --version): Rolling upgrade from <7.3 to ≥7.10

Description of the problem including expected versus actual behavior:

We have special handling for mapping the new pluggable master/data/ingest roles onto their legacy counterparts when talking to pre-7.3 nodes which did not support pluggable roles:

elasticsearch/server/src/main/java/org/elasticsearch/cluster/node/DiscoveryNode.java

Lines 332 to 344 in 941b028

	// an old node will only understand legacy roles since pluggable roles is a new concept
	final List<DiscoveryNodeRole> rolesToWrite =
	roles.stream().filter(DiscoveryNodeRole.LEGACY_ROLES::contains).collect(Collectors.toList());
	out.writeVInt(rolesToWrite.size());
	for (final DiscoveryNodeRole role : rolesToWrite) {
	if (role == DiscoveryNodeRole.MASTER_ROLE) {
	out.writeEnum(LegacyRole.MASTER);
	} else if (role == DiscoveryNodeRole.DATA_ROLE) {
	out.writeEnum(LegacyRole.DATA);
	} else if (role == DiscoveryNodeRole.INGEST_ROLE) {
	out.writeEnum(LegacyRole.INGEST);
	}
	}

However this code does not use DiscoveryNodeRole#getCompatibilityRole() so it does not map the data-tiers-related roles DATA_{HOT,WARM,COLD,FROZEN} onto the legacy data role.

Relates #60994 and #63581 so I'm labelling this similarly.

[elasticmachine]

Pinging @elastic/es-core-features (Team:Core/Features)

[andreidan]

Closing as fixed by #71628