SOLR docs - clarify conf_dir location

[gilzow]

Where on docs.platform.sh should be changed?

https://docs.platform.sh/add-services/solr.html#solr-6-and-later
https://docs.upsun.com/add-services/solr.html#solr-6-and-later

What exactly should be updated?

In the SOLR 4 section we have an example:

  configuration:
    core_config: !archive "DIRECTORY"

and then state:

DIRECTORY points to a directory in the Git repository, in or below the .platform/ folder. This directory needs to contain everything that Solr needs to start a core. At the minimum, solrconfig.xml and schema.xml.

For example, place them in .platform/solr/conf/ such that the schema.xml file is located at .platform/solr/conf/schema.xml. You can then reference that path like this -

solr:
  type: "solr:4.10"
  disk: 1024
  configuration:
    core_config: !archive "solr/conf/"

But in the SOLR 6 and later section we don't include a similar explanation for conf_dir key.

We kind of address it in the first example, but not directly. The example also covers multiple cores so the point about conf_dir can be easily overlooked.

We should probably rewrite the example to use the same DIRECTORY token with a full explanation.

Additional context

https://platformsh.slack.com/archives/C022N5Q5LDP/p1753807924220219