Fix urls in NeptuneLogger docstring

Neptune updated their API and docs to version 3.X. This commit
fixes the urls in the NeptuneLogger docstring to point to the
correct version 2.X legacy docs.

Author: aknierim

src/lightning/pytorch/loggers/neptune.py

@@ -37,7 +37,7 @@
 
 
 class NeptuneLogger(Logger):
-    r"""Log using `Neptune <https://docs.neptune.ai/integrations/lightning/>`_.
+    r"""Log using `Neptune <https://docs-legacy.neptune.ai/integrations/lightning/>`_.
 
     Install it with pip:
 
@@ -97,7 +97,7 @@ def any_lightning_module_function_or_hook(self):
     Note that the syntax ``self.logger.experiment["your/metadata/structure"].append(metadata)`` is specific to
     Neptune and extends the logger capabilities. It lets you log various types of metadata, such as
     scores, files, images, interactive visuals, and CSVs.
-    Refer to the `Neptune docs <https://docs.neptune.ai/logging/methods>`_
+    Refer to the `Neptune docs <https://docs-legacy.neptune.ai/logging/methods>`_
     for details.
     You can also use the regular logger methods ``log_metrics()``, and ``log_hyperparams()`` with NeptuneLogger.
 
@@ -152,7 +152,7 @@ def any_lightning_module_function_or_hook(self):
         )
         trainer = Trainer(max_epochs=3, logger=neptune_logger)
 
-    Check `run documentation <https://docs.neptune.ai/api/neptune/#init_run>`_
+    Check `run documentation <https://docs-legacy.neptune.ai/api/neptune/#init_run>`_
     for more info about additional run parameters.
 
     **Details about Neptune run structure**
@@ -164,18 +164,18 @@ def any_lightning_module_function_or_hook(self):
 
     See also:
         - Read about
-          `what objects you can log to Neptune <https://docs.neptune.ai/logging/what_you_can_log/>`_.
+          `what objects you can log to Neptune <https://docs-legacy.neptune.ai/logging/what_you_can_log/>`_.
         - Check out an `example run <https://app.neptune.ai/o/common/org/pytorch-lightning-integration/e/PTL-1/all>`_
           with multiple types of metadata logged.
         - For more detailed examples, see the
-          `user guide <https://docs.neptune.ai/integrations/lightning/>`_.
+          `user guide <https://docs-legacy.neptune.ai/integrations/lightning/>`_.
 
     Args:
         api_key: Optional.
             Neptune API token, found on https://www.neptune.ai upon registration.
             You should save your token to the `NEPTUNE_API_TOKEN`
             environment variable and leave the api_key argument out of your code.
-            Instructions: `Setting your API token <https://docs.neptune.ai/setup/setting_api_token/>`_.
+            Instructions: `Setting your API token <https://docs-legacy.neptune.ai/setup/setting_api_token/>`_.
         project: Optional.
             Name of a project in the form "workspace-name/project-name", for example "tom/mask-rcnn".
             If ``None``, the value of `NEPTUNE_PROJECT` environment variable is used.
@@ -251,7 +251,7 @@ def training_step(self, batch, batch_idx):
         is specific to Neptune and extends the logger capabilities.
         It lets you log various types of metadata, such as scores, files,
         images, interactive visuals, and CSVs. Refer to the
-        `Neptune docs <https://docs.neptune.ai/logging/methods>`_
+        `Neptune docs <https://docs-legacy.neptune.ai/logging/methods>`_
         for more detailed explanations.
         You can also use the regular logger methods ``log_metrics()``, and ``log_hyperparams()``
         with NeptuneLogger.