Consider adding more Rat assemblies

**Source UCSC**

GRCr8
UTH_Rnor_SHR_Utx
UTH_Rnor_WKY_Bbb_1.0

Request at https://help.galaxyproject.org/t/newly-launched-bn-rat-genome-assembly-grcr8-into-the-reference-genome-list/15778
> Hi, may I ask a favor that if anyone could put the newly launched BN rat genome assembly GRCr8 (if possible also the other two assemblies? Rat UTH_Rnor_SHR_Utx and Rat UTH_Rnor_WKY_Bbb_1.0?) into the Galaxy reference genome list? There are a few changes in the rat GRCr8 compared to the former rt7.2 assembly. Which would be interesting to map with my RNA sequencing data. Thanks in advance!

Psss **For end users!**
You can use these _right now_. Go to the UCSC Downloads area, copy the genome and annotation into Galaxy, and use the [Custom Genome ](https://training.galaxyproject.org/training-material/faqs/galaxy/reference_genomes_custom_genomes.html)functions! :)

Start by reviewing the repository contents and the UCSC assemblies named in the issue: GRCr8, UTH_Rnor_SHR_Utx, and UTH_Rnor_WKY_Bbb_1.0. Identify where Galaxy reference-genome entries are maintained and what validation or update process is used. Done means the requested rat assemblies are available in the reference genome list and can be selected for Galaxy workflows.

Written by the indexing model from the issue text.