Allowlist for domains on the `google_search` tool

**Is your feature request related to a problem? Please describe.**
The client at which I'm currently working has strict egress policies. Effectively, we create an allowlist for domains to which our services may make requests. Consequently, using tools like `google_search` within the ADK framework is a bit tricky, as we can only specify a blocklist.

**Describe the solution you'd like**
An specifiable allowlist for web domains for the Google Search tool.

**Describe alternatives you've considered**
N/A

**Additional context**

I was redirected from [this issue](https://github.com/google/adk-python/issues/5460)