Add --debug-query-plans (#1187)

* Add --debug-query-plans

* change order to alphabetical

* change default to false

* add note on how to use new flag

---------

Co-authored-by: katarinasupe <supe.katarina@gmail.com>

Author: Ignition

pages/database-management/configuration.mdx

@@ -489,6 +489,7 @@ This section contains the list of all other relevant flags used within Memgraph.
 | `--also-log-to-stderr=false`                    | Log messages go to stderr in addition to logfiles.                                                                                                                                                                                                                                                                                                           | `[bool]`   |
 | `--data-directory=/var/lib/memgraph`            | Path to directory in which to save all permanent data.                                                                                                                                                                                                                                                                                                       | `[string]` |
 | `--data-recovery-on-startup=true`               | Facilitates recovery of one or more individual databases and their contents during startup. Replaces `--storage-recover-on-startup`                                                                                                                                                                                                                          | `[bool]`   |
+| `--debug-query-plans=false`                      | Enable DEBUG logging of potential query plans.                                         | `[string]` |
 | `--delta-chain-cache-threshold=128`             | The minimum number of deltas worth caching when rebuilding a certain object's state. Useful when executing parallel transactions dependant on changes of a frequently changed graph object, to lower CPU usage. Must be a positive non-zero integer.                                                                                                         | `[uint64]` |
 | `--flag-file`                                   | Path to the additional configuration file, overrides the default configuration settings.                                                                                                                                                                                                                                                                     | `[string]` |
 | `--help`                                        | Show help on all flags and exit. The default values is `false`.                                                                                                                                                                                                                                                                                              | `[bool]`   |

pages/database-management/logs.mdx

@@ -26,6 +26,11 @@ You can check the log level by running `SHOW DATABASE SETTING "log.level";` quer
 To access the logs from the Memgraph Lab interface, make sure to expose the port
 7444 when starting Memgraph with Docker. 
 
+<Callout type="info">
+To get additional information on the generated query plans, set
+`--debug-query-plans` to `True`, along with `--log-level` set to `DEBUG` or `TRACE`.
+</Callout>
+
 ## Access logs
 
 If you installed Memgraph with Linux, logs can be found in the

pages/querying/best-practices.mdx

@@ -96,6 +96,11 @@ nonsense or sales pitch, just tech.
   />
 </Cards>
 
+To prepare the information we need to help you debug the issue, it is best to
+have `--log-level` set to `TRACE` along with the `--debug-query-plans` set to `True`.
+That will provide better diagnostics to identify poor cost modelling over
+generated plans and hence poor plan selection.
+
 ## How to speed up query execution
 
 Before diving into the details of the query execution optimization, it is