deprecate --agency.pool-size startup option (#1171)

* deprecate --agency.pool-size startup option

* Review

Co-authored-by: Simran Spiller <simran@arangodb.com>
Co-authored-by: Paula Mihu <97217318+nerpaula@users.noreply.github.com>

Author: 3 people

3.11/programs-arangod-agency.md

@@ -40,9 +40,11 @@ Which address to advertise to the outside.
 
 ## Pool size
 
+<small>Deprecated in: v3.11.0</small>
+
 `agency.pool-size`
 
-Number of Agent pool.
+Number of Agents in pool.
 
 ## Size
 

3.11/release-notes-upgrading-changes311.md

@@ -2,16 +2,14 @@
 layout: default
 description: It is recommended to check the following list of incompatible changes before upgrading to ArangoDB 3.11
 ---
-Incompatible changes in ArangoDB 3.11
-=====================================
+# Incompatible changes in ArangoDB 3.11
 
 It is recommended to check the following list of incompatible changes **before**
 upgrading to ArangoDB 3.11, and adjust any client programs if necessary.
 
 The following incompatible changes have been made in ArangoDB 3.11:
 
-Restriction of indexable fields
--------------------------------
+## Restriction of indexable fields
 
 It is now forbidden to create indexes that cover fields whose attribute names
 start or end with `:` , for example, `fields: ["value:"]`. This notation is
@@ -20,8 +18,18 @@ reserved for internal use.
 Existing indexes are not affected but you cannot create new indexes with a
 preceding or trailing colon.
 
-Client tools
-------------
+## Startup options
+
+### `--agency.pool-size` deprecated
+
+The `--agency.pool-size` option was effectively not properly supported in any
+version of ArangoDB. Setting the option to anything but the value of
+`--agency.size` should be avoided.
+
+From v3.11.0 onwards, this option is deprecated, and setting it to a value
+different than the value of `--agency.size` leads to a startup error.
+
+## Client tools
 
 ### arangoexport