SolrConnectorPluginBase::getServerUri() returns incorrect information on edit form

Problem/Motivation

The Search API server edit form displays the Solr server URI as follows through \Drupal\search_api_solr\Plugin\search_api\backend\SearchApiSolrBackend:

$form['server_description'] = [
  '#type' => 'item',
   '#title' => $this->t('Solr server URI'),
  '#description' => $this->getSolrConnector()->getServerLink(),
];

The server link is generated by replacing the localhost with the $_SERVER['SERVER_NAME']. However, the server name global is incorrect for servers behind a load balancer, for example http://localhost turns into http://~^uu(0(3|4)|)\\.nl$:8983/, which is misleading.

Furthermore, the $configuration object in \Drupal\search_api_solr\SolrConnector\SolrConnectorPluginBase does not include configuration overrides. A typical way to implement different Solr backend for different environments is to apply a configuration override in settings.php, for example:

$config['search_api.server.solr']['backend_config']['connector_config']['host'] = 'solr-test.combell.net';

This URL is then reflected in the user interface on the server canonical page, but not its edit form.

Proposed resolution

1. Remove the 'smart' formatting in getServerUri()
2. Account for configuration overrides in \Drupal\search_api_solr\SolrConnector\SolrConnectorPluginBase OR do not display the Solr server URI on the edit form

Remaining tasks

1. Write a patch
2. Review
3. Commit

User interface changes

To be determined.

API changes

None.

Data model changes

None.