Feature: Add context to requests for custom API services.

[lnikonl]

Feature:
Add context to requests for custom API services.

Use case:
When using LLM models for a custom dictionary, the translation quality will be more accurate if the context is added to the query.
And it is possible to use it as part of the prompt.

Changed:

• Add 'context' field in SearchApiRequest.
  app/Http/Requests/Dictionaries/SearchApiRequest.php

        return [
            'language' => 'required|string',
            'term' => 'required|string',
            'context' => 'string',
        ];

• Add 'ctx' field for request to custom api.
  app/Services/DictionaryService.php

private function buildCustomApiTranslateRequest(Pool $pool, Dictionary $dictionary, string $term, string $context): void
{
    $pool->post($dictionary->api_host, [
        'q' => $term,
        'ctx' => $context,
        'source' => strtolower($dictionary->source_language),
        'target' => strtolower($dictionary->target_language),
    ]);
}

• Some changes in code for support it.