Add TCM dev mode, slab stats, tt console (#4618)

Resolves #3902 #4251 #4252

Author: p7nov

doc/tooling/tcm/index.rst

@@ -44,5 +44,6 @@ to read data. LDAP authorization is supported as well.
     tcm_audit_log
     tcm_configuration
     tcm_backend_store
+    tcm_dev_mode
     tcm_configuration_reference
     Releases <tcm_releases/index>

doc/tooling/tcm/tcm_cluster_management/tcm_cluster_state.rst

@@ -99,14 +99,20 @@ To view the detailed information about an instance or connect to it, click the c
 row in the instances list or a vertex of the graph. On the instance page, you can
 find:
 
-*   its configuration overview
+*   the instance configuration overview
 *   current state (with warning and error messages if any)
 *   the detailed Tarantool information returned by the instance introspection functions
     from :ref:`box.info <box_introspection-box_info>`, :ref:`box.stat <box_introspection-box_stat>`,
-    and other built-in modules.
-
-Additionally, on the instance details page there is a terminal in which you can execute
-arbitrary Lua code on the instance.
+    and other built-in modules
+*   memory usage by the :ref:`slab allocator <memtx-memory>`
+*   instance users and roles
+*   stored functions
+*   instance metrics
+
+The page also provides Lua and SQL terminals to execute built-in functions
+and requests on the instance. You can choose between two Lua terminals: the
+:ref:`tt interactive console <tt-interactive-console>` with code completion and highlighting or
+the default :ref:`Tarantool console <interactive_console>`.
 
 ..  _tcm_cluster_state_urls:
 

doc/tooling/tcm/tcm_dev_mode.rst

@@ -0,0 +1,69 @@
+..  _tcm_dev_mode:
+
+Development mode
+================
+
+..  include:: index.rst
+    :start-after: ee_note_tcm_start
+    :end-before: ee_note_tcm_end
+
+|tcm_full_name| provides a special mode aimed to use during the development.
+This mode extends the web interface with capabilities that can help in development
+or testing environments, such as starting and stopping instances or instance promotion.
+
+..  _tcm_dev_mode_enable:
+
+Enabling development mode
+-------------------------
+
+You can enable |tcm| development mode in different ways: in its web interface,
+in the configuration file, using an environment variable, or using a command-line option.
+
+..  _tcm_dev_mode_enable_web:
+
+Web interface
+~~~~~~~~~~~~~
+
+To enable development mode on the running |tcm| instance, use its :ref:`web interface <tcm_ui_overview>`:
+
+#.  Open user settings: click **Settings** under the user name in the header.
+#.  Go to the **About** tab.
+#.  Click the toggle button beside **tcm/mode**.
+
+..  _tcm_dev_mode_enable_config:
+
+Configuration file
+~~~~~~~~~~~~~~~~~~
+
+To start |tcm| in the development mode, specify the ``mode: development`` option
+in its :ref:`configuration file <tcm_configuration>`:
+
+.. code-block:: yaml
+
+    # tcm_config.yaml
+    mode: development
+
+..  _tcm_dev_mode_enable_cli:
+
+Command-line option
+~~~~~~~~~~~~~~~~~~~
+
+To start |tcm| in the development mode, specify the ``--mode=development`` command-line option:
+
+.. code-block:: console
+
+    $ tcm --mode=development
+
+
+..  _tcm_dev_mode_enable_env:
+
+Environment variable
+~~~~~~~~~~~~~~~~~~~~
+
+To make new |tcm| instances start in the development mode by default, set the
+``TCM_MODE`` environment variable to ``development``:
+
+.. code-block:: console
+
+    $ export TCM_MODE=development
+    $ tcm

doc/tooling/tcm/tcm_ui_overview.rst

@@ -72,10 +72,11 @@ Page visibility
 ---------------
 
 This overview describes most |tcm| pages. The exact set of pages and controls available
-to a particular are determined by the user's :ref:`permissions <tcm_access_control_permissions>`.
+to a particular user is determined by the user's :ref:`permissions <tcm_access_control_permissions>`.
 
 Some features, such as data schema editing, are available only in the **development** mode.
 You can switch to it in the :ref:`user settings <tcm_ui_user_settings>` of the **Default Admin** user.
+To learn more about the development mode, see :ref:`tcm_dev_mode`.
 
 ..  _tcm_ui_groups: