add uppercase token filter docs opensearch-project#8452

Signed-off-by: Anton Rubin <[email protected]>

_analyzers/token-filters/index.md

@@ -60,6 +60,6 @@ Normalization | `arabic_normalization`: [ArabicNormalizer](https://lucene.apache
 `trim` | [TrimFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/TrimFilter.html) | Trims leading and trailing white space from each token in a stream. 
 `truncate` | [TruncateTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/TruncateTokenFilter.html) | Truncates tokens whose length exceeds the specified character limit. 
 `unique` | N/A | Ensures each token is unique by removing duplicate tokens from a stream. 
-`uppercase` | [UpperCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/LowerCaseFilter.html) | Converts tokens to uppercase. 
+[`uppercase`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/uppercase/) | [UpperCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/LowerCaseFilter.html) | Converts tokens to uppercase. 
 `word_delimiter` | [WordDelimiterFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/WordDelimiterFilter.html) | Splits tokens at non-alphanumeric characters and performs normalization based on the specified rules. 
 `word_delimiter_graph` | [WordDelimiterGraphFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/WordDelimiterGraphFilter.html) | Splits tokens at non-alphanumeric characters and performs normalization based on the specified rules. Assigns multi-position tokens a `positionLength` attribute.

_analyzers/token-filters/uppercase.md

@@ -0,0 +1,83 @@
+---
+layout: default
+title: Uppercase
+parent: Token filters
+nav_order: 460
+---
+
+# Uppercase token filter
+
+The `uppercase` token filter is used to convert all tokens (words) to uppercase during analysis.
+
+## Example
+
+The following example request creates a new index named `uppercase_example` and configures an analyzer with `uppercase` filter:
+
+```json
+PUT /uppercase_example
+{
+  "settings": {
+    "analysis": {
+      "filter": {
+        "uppercase_filter": {
+          "type": "uppercase"
+        }
+      },
+      "analyzer": {
+        "uppercase_analyzer": {
+          "type": "custom",
+          "tokenizer": "standard",
+          "filter": [
+            "lowercase",
+            "uppercase_filter"
+          ]
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Generated tokens
+
+Use the following request to examine the tokens generated using the analyzer:
+
+```json
+GET /uppercase_example/_analyze
+{
+  "analyzer": "uppercase_analyzer",
+  "text": "OpenSearch is powerful"
+}
+```
+{% include copy-curl.html %}
+
+The response contains the generated tokens:
+
+```json
+{
+  "tokens": [
+    {
+      "token": "OPENSEARCH",
+      "start_offset": 0,
+      "end_offset": 10,
+      "type": "<ALPHANUM>",
+      "position": 0
+    },
+    {
+      "token": "IS",
+      "start_offset": 11,
+      "end_offset": 13,
+      "type": "<ALPHANUM>",
+      "position": 1
+    },
+    {
+      "token": "POWERFUL",
+      "start_offset": 14,
+      "end_offset": 22,
+      "type": "<ALPHANUM>",
+      "position": 2
+    }
+  ]
+}
+```