Add OSS Index Base URL configuration field

Adds configurable Base URL field to the OSS Index analyzer admin UI,
allowing users to point to alternative OSS Index API endpoints
(e.g., https://api.guide.sonatype.com).

Implementation follows the established pattern from Snyk and Trivy
analyzers for consistency:
- Uses b-validated-input-group-form-input component
- Implements required field validation with lazy evaluation
- Integrates with configPropertyMixin for API communication
- Property: scanner.ossindex.base.url (default: https://ossindex.sonatype.org)

The Base URL field appears between Alias Sync and Username fields,
maintaining logical grouping of configuration options.

Related backend PR: DependencyTrack/dependency-track#5736

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Brian Fox <brianf@sonatype.com>

Author: brianf

src/views/administration/analyzers/OssIndexAnalyzer.vue

@@ -20,6 +20,14 @@
         :title="$t('admin.vulnsource_alias_sync_enable_tooltip')"
       />
       {{ $t('admin.vulnsource_alias_sync_enable') }}
+      <b-validated-input-group-form-input
+        id="ossindex-baseUrl"
+        :label="$t('admin.base_url')"
+        input-group-size="mb-3"
+        rules="required"
+        v-model="baseUrl"
+        lazy="true"
+      />
       <b-validated-input-group-form-input
         id="ossindex-username"
         :label="$t('admin.registered_email_address')"
@@ -68,6 +76,7 @@ export default {
     return {
       scannerEnabled: false,
       aliasSyncEnabled: false,
+      baseUrl: '',
       username: '',
       apitoken: '',
       labelIcon: {
@@ -89,6 +98,11 @@ export default {
           propertyName: 'ossindex.alias.sync.enabled',
           propertyValue: this.aliasSyncEnabled,
         },
+        {
+          groupName: 'scanner',
+          propertyName: 'ossindex.base.url',
+          propertyValue: this.baseUrl,
+        },
         {
           groupName: 'scanner',
           propertyName: 'ossindex.api.username',
@@ -116,6 +130,9 @@ export default {
           case 'ossindex.alias.sync.enabled':
             this.aliasSyncEnabled = common.toBoolean(item.propertyValue);
             break;
+          case 'ossindex.base.url':
+            this.baseUrl = item.propertyValue;
+            break;
           case 'ossindex.api.username':
             this.username = item.propertyValue;
             break;