MINOR. Update Epoch field descrition in FetchRequest api doc
The `Epoch` field description was copy of the `SessionId` field. This
change updates it to describe `Epoch` instead.
No code change, only description changes. Code compiles.
Reviewers: Jason Gustafson
{ "name": "SessionId", "type": "int32", "versions": "7+", "default": "0", "ignorable": false,
"about": "The fetch session ID." },
{ "name": "Epoch", "type": "int32", "versions": "7+", "default": "-1", "ignorable": false,
- "about": "The fetch session ID." },
+ "about": "The epoch of the partition leader as known to the follower replica or a consumer." },
{ "name": "Topics", "type": "[]FetchableTopic", "versions": "0+",
"about": "The topics to fetch.", "fields": [
{ "name": "Name", "type": "string", "versions": "0+", "entityType": "topicName",
