docs(javascript): Change default value for maxValueLength (#15349)

## DESCRIBE YOUR PR

PR getsentry/sentry-javascript#18043 removed the
default value of `maxValueLength`

part of getsentry/sentry-javascript#17389
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Author: s1gr1d

docs/platforms/javascript/common/configuration/options.mdx

@@ -136,7 +136,7 @@ Sentry.init({
 
 </SdkOption>
 
-<SdkOption name="maxValueLength" type='number' defaultValue='250'>
+<SdkOption name="maxValueLength" type='number'>
 
 Maximum number of characters every string property on events sent to Sentry can have before it will be truncated.
 

docs/platforms/javascript/common/troubleshooting/index.mdx

@@ -57,7 +57,7 @@ For more details, see the [full documentation on Event Payload](https://develop.
 
 <Expandable permalink title="Max JSON payload size">
 
-`maxValueLength` has a default value of 250, but you can adjust this value according to your needs if your messages are longer. Please note that not every single value is affected by this option.
+By default, `maxValueLength` is undefined and nothing is truncated, but you can change this value according to your needs if your messages are longer (for example, to `250`). Please note that not every single value is affected by this option.
 
 </Expandable>