[FR] Allow poolsize and maxpool size settings for http client

Start at the HttpClient constructor shown in the issue and inspect how its requests.Session mounts HTTPAdapter instances for both schemes. Trace the existing retry, timeout, and session setup, then verify that configurable pool settings are applied consistently to HTTP and HTTPS requests and that the client behavior remains unchanged by default.

Is your feature request related to a problem? Please describe.
I am currently facing a performance issue in which the default max pool size of requests library has become a bottleneck.

Describe the solution you'd like
A clear and concise description of what you want to happen.
I was wondering if we could increase the pool size by taking them as parameters for message client constructor
Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context

class HttpClient:
    def __init__(
            self, credential=None, session=None, base_url='', headers=None,
            retries=DEFAULT_RETRY_CONFIG, timeout=DEFAULT_TIMEOUT_SECONDS,
            pool_connections=DEFAULT_POOL_CONNECTIONS, pool_maxsize=DEFAULT_MAX_POOL_SIZE
        ):
        if credential:
            self._session = transport.requests.AuthorizedSession(credential)
        elif session:
            self._session = session
        else:
            self._session = requests.Session() # pylint: disable=redefined-variable-type

        if headers:
            self._session.headers.update(headers)
        if retries:
            self._session.mount('http://', requests.adapters.HTTPAdapter(max_retries=retries))
            self._session.mount('https://', requests.adapters.HTTPAdapter(max_retries=retries))
        
        self._session.mount('http://', requests.adapters.HTTPAdapter(pool_connections=pool_connections, pool_maxsize=pool_maxsize))
         self._session.mount('https://', requests.adapters.HTTPAdapter(pool_connections=pool_connections, pool_maxsize=pool_maxsize))
        
        self._base_url = base_url
        self._timeout = timeout