Update documentation for GFF schema for Alias field

[a-li]

What changes are proposed in this pull request?

Update documentation for GFF schema for Alias field

According to https://glow.readthedocs.io/en/latest/etl/gff.html#schema. Alias is defined as string. However, in the actual source code, it's defined as an array of string:

glow/core/src/main/scala/io/projectglow/common/schemas.scala

Line 171 in 8b0bcd6

val aliasField = StructField("alias", ArrayType(StringType))

Updating the documentation so it is matching exactly how it's internally represented.

How is this patch tested?

• Unit tests
• Integration tests
• Manual tests

(Details)