docs: document gzip default and brotli extra for request compression (#1209)

Closes: #1179

The `compression` docstring on `ApifyClient` / `ApifyClientAsync` did
not say what the default is or that `'brotli'` needs an optional extra.
That made the difference from the JS client (which defaults to brotli
via `node:zlib`) hard to discover.

---

Co-authored-by: Vlada Dusek <v.dusek96@gmail.com>

Author: dheerajitbhu

src/apify_client/_apify_client.py

@@ -154,11 +154,14 @@ def __init__(
             user_agent_suffix: Extra part or parts appended to the default `User-Agent` header, separated by `; `, for
                 example to identify the tool built on top of the client. With `with_custom_http_client`, pass it to
                 the HTTP client's constructor.
-            compression: Compression algorithm for request bodies. Pass a string literal to select an algorithm,
-                or an `HttpCompressor` instance for finer-grained control.
+            compression: Compression algorithm for request bodies. Defaults to `'gzip'`. Pass a string literal to select
+                an algorithm, or an `HttpCompressor` instance for finer-grained control. `'brotli'` needs the `brotli`
+                extra (`pip install "apify-client[brotli]"`). It is not the default because the `brotli` package is a C
+                extension, while gzip support is part of the Python standard library.
 
         Raises:
             ValueError: If `max_retries` is negative.
+            ImportError: If `compression` is `'brotli'` and the `brotli` extra is not installed.
         """
         if max_retries < 0:
             raise ValueError(f'max_retries must be a non-negative integer, got {max_retries}')
@@ -534,11 +537,14 @@ def __init__(
             user_agent_suffix: Extra part or parts appended to the default `User-Agent` header, separated by `; `, for
                 example to identify the tool built on top of the client. With `with_custom_http_client`, pass it to
                 the HTTP client's constructor.
-            compression: Compression algorithm for request bodies. Pass a string literal to select an algorithm,
-                or an `HttpCompressor` instance for finer-grained control.
+            compression: Compression algorithm for request bodies. Defaults to `'gzip'`. Pass a string literal to select
+                an algorithm, or an `HttpCompressor` instance for finer-grained control. `'brotli'` needs the `brotli`
+                extra (`pip install "apify-client[brotli]"`). It is not the default because the `brotli` package is a C
+                extension, while gzip support is part of the Python standard library.
 
         Raises:
             ValueError: If `max_retries` is negative.
+            ImportError: If `compression` is `'brotli'` and the `brotli` extra is not installed.
         """
         if max_retries < 0:
             raise ValueError(f'max_retries must be a non-negative integer, got {max_retries}')