Endwith dont need to be checked with string literal

`//.` and `.` should end in the same way

Also address review comment about `['//.']` -> `"//."`

quickwit/quickwit-doc-mapper/src/default_doc_mapper/default_mapper.rs

@@ -127,10 +127,10 @@ fn validate_timestamp_field(
     timestamp_field_path: &str,
     mapping_root_node: &MappingNode,
 ) -> anyhow::Result<()> {
-    if timestamp_field_path.starts_with('.') || timestamp_field_path.starts_with(['\\', '.']) {
+    if timestamp_field_path.starts_with('.') || timestamp_field_path.starts_with("\\.") {
         bail!("Timestamp field `{timestamp_field_path}` should not start with a `.`.");
     }
-    if timestamp_field_path.ends_with('.') || timestamp_field_path.ends_with(['\\', '.']) {
+    if timestamp_field_path.ends_with('.') {
         bail!("Timestamp field `{timestamp_field_path}` should not end with a `.`.");
     }
     let Some(timestamp_field_type) =
@@ -275,10 +275,10 @@ impl TryFrom<DefaultDocMapperBuilder> for DefaultDocMapper {
 /// - if str, the field must use the `raw` tokenizer for indexing.
 /// - the field must be indexed.
 fn validate_tag(tag_field_name: &str, schema: &Schema) -> Result<(), anyhow::Error> {
-    if tag_field_name.starts_with('.') || tag_field_name.starts_with(['\\', '.']) {
+    if tag_field_name.starts_with('.') || tag_field_name.starts_with("\\.") {
         bail!("Tag field `{tag_field_name}` should not start with a `.`.");
     }
-    if tag_field_name.ends_with('.') || tag_field_name.ends_with(['\\', '.']) {
+    if tag_field_name.ends_with('.') {
         bail!("Tag field `{tag_field_name}` should not end with a `.`.");
     }
     let field = schema