ESQL: Mark a few features as experimental (#105263)

Mark the following features as experimental in the docs:
* `AUTO_BUCKET()`
* `SHOW FUNCTIONS`
* unsigned_long type

docs/reference/esql/esql-limitations.asciidoc

@@ -32,7 +32,7 @@ include::processing-commands/limit.asciidoc[tag=limitation]
 * `long`
 * `null`
 * `text`
-* `unsigned_long`
+* experimental:[] `unsigned_long`
 * `version`
 * Spatial types
 ** `geo_point`

docs/reference/esql/functions/auto_bucket.asciidoc

@@ -2,6 +2,8 @@
 [[esql-auto_bucket]]
 === `AUTO_BUCKET`
 
+experimental::[]
+
 *Syntax*
 
 [source,esql]

docs/reference/esql/functions/date-time-functions.asciidoc

@@ -8,7 +8,7 @@
 {esql} supports these date-time functions:
 
 // tag::date_list[]
-* <<esql-auto_bucket>>
+* experimental:[] <<esql-auto_bucket>>
 * <<esql-date_diff>>
 * <<esql-date_extract>>
 * <<esql-date_format>>

docs/reference/esql/functions/to_unsigned_long.asciidoc

@@ -2,6 +2,8 @@
 [[esql-to_unsigned_long]]
 === `TO_UNSIGNED_LONG`
 
+experimental::[]
+
 *Aliases*
 
 `TO_ULONG`, `TO_UL`

docs/reference/esql/functions/type-conversion-functions.asciidoc

@@ -21,7 +21,7 @@
 * <<esql-to_long>>
 * <<esql-to_radians>>
 * <<esql-to_string>>
-* <<esql-to_unsigned_long>>
+* experimental:[] <<esql-to_unsigned_long>>
 * <<esql-to_version>>
 // end::type_list[]
 

docs/reference/esql/source-commands/show.asciidoc

@@ -12,7 +12,7 @@ SHOW item
 *Parameters*
 
 `item`::
-Can be `INFO` or `FUNCTIONS`.
+Can be `INFO` or experimental:[] `FUNCTIONS`.
 
 *Description*
 
@@ -20,7 +20,7 @@ The `SHOW` source command returns information about the deployment and
 its capabilities:
 
 * Use `SHOW INFO` to return the deployment's version, build date and hash.
-* Use `SHOW FUNCTIONS` to return a list of all supported functions and a
+* Use experimental:[] `SHOW FUNCTIONS` to return a list of all supported functions and a
 synopsis of each function.
 
 *Examples*