Better Instructions for Updating Metadata Blocks, how to handle Solr updates in PRs

[djbrooke]

When working on #7810 it was suggested that we would benefit from outlining the process/expectations for a contributor making a metadata block update. Possible areas to add content:

• https://guides.dataverse.org/en/5.8/admin/metadatacustomization.html#updating-the-solr-schema
• https://guides.dataverse.org/en/5.8/developers/tips.html#solr

Happy to serve as a test case for this, as I've learned a lot over the last few days myself. We have another test case for these instructions coming up in #8127.

[djbrooke]

• There may be some question about whether or not we want to use a script for this and improve the script
• Is there information out there in documents that should be included (out of scope)