chore: Add Browser agent v1.258.1 release notes

src/content/docs/release-notes/new-relic-browser-release-notes/browser-agent-release-notes/browser-agent-v1.258.1.mdx

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+---
+subject: Browser agent
+releaseDate: "2024-05-07"
+version: 1.258.1
+features: []
+bugs: ["Improve Error Casting","Run inside cross-origin iframes for firefox/safari","Exclude data url requests as captured AJAX events","Session trace nodes de-duplication","Remove API start()'s features param"]
+security: []
+---
+
+## v1.258.1
+
+### Bug fixes
+
+#### Improve Error Casting
+Improve detection of line and column to allow errors that throw without a stack -- such as some chrome errors -- to still get basic error location information
+
+#### Run inside cross-origin iframes for firefox/safari
+Resolve a bug that prevented the agent from running in cross-origin iFrames for Firefox and Safari due to how the browsers implement context security.
+
+#### Exclude data url requests as captured AJAX events
+Do not report XMLHttpRequest or fetch calls made for data urls. The event and metric created for data urls are sparse and unhelpful, so they are no longer being captured or sent.
+
+#### Session trace nodes de-duplication
+Remove duplicated error and event nodes in traces. Each error noticed by the JS errors feature will now only be 1 node instead of 3. Each occurrence of any event fired on for a DOM node or XMLHttpRequest object is pared down to 1 instead of being directly proportional to the number of subscribed listeners.
+
+#### Remove API start()'s features param
+The `start()` method in agent API no longer accepts an argument. It will forcibly start all features that were marked `autoStart: false` in the configuration that has not yet started when it is called. If `page_view_event` had this property set to false, the agent will not send anything until `start` is called.
+
+## Support statement
+
+New Relic recommends that you upgrade the agent regularly to ensure that you're getting the latest features and performance benefits. Older releases will no longer be supported when they reach [end-of-life](https://docs.newrelic.com/docs/browser/browser-monitoring/getting-started/browser-agent-eol-policy/). Release dates are reflective of the original publish date of the agent version.
+
+New browser agent releases are rolled out to customers in small stages over a period of time. Because of this, the date the release becomes accessible to your account may not match the original publish date. Please see this [status dashboard](https://newrelic.github.io/newrelic-browser-agent-release/) for more information.
+
+Consistent with our [browser support policy](https://docs.newrelic.com/docs/browser/new-relic-browser/getting-started/compatibility-requirements-browser-monitoring/#browser-types), v1.258.1 of the Browser agent was built for and tested against these browsers and version ranges: Chrome 115-124, Edge 115-123, Safari 16-17, and Firefox 116-125. For mobile devices, v1.251.1 was built and tested for Android Chrome 100-124 and iOS Safari 15.5-16.2.