docs: add analytics migration guidance for web and JavaScript platforms

[soberm]

Description of changes

The analytics portion of the Pinpoint migration guide now covers the web and JavaScript platforms: javascript, react, angular, nextjs, vue, and react-native.

The guide's ## Migrate analytics event recording heading applies to every platform in meta.platforms, but its body was scoped to ['android', 'flutter', 'swift']. The mobile libraries document the Kinesis and Firehose providers at analytics/kinesis/ and analytics/firehose/, which are mobile-only pages, so the links could not be shared with the web platforms. As a result the heading rendered with no body on the web platforms — for example on the react page.

This adds a sibling <InlineFilter> block with the equivalent guidance for the JavaScript library, which reaches the same two services through different pages:

• Amazon Kinesis → Streaming analytics data
• Amazon Data Firehose → Storing analytics data

The new section walks through the amplify-js specifics:

• Moving record and flushEvents to the aws-amplify/analytics/kinesis and aws-amplify/analytics/kinesis-firehose subpaths.
• Mapping the Pinpoint event name, attributes, and metrics into the data blob written to the stream, with the Kinesis streamName and partitionKey. Firehose records take streamName only.
• Passing stream coordinates in configureAutoTrack options, since automatically tracked events need a destination.
• Directing identifyUser to Amazon Connect Customer Profiles, because the streaming providers record events only and do not expose an identifyUser API.

The API surface and input shapes were verified against the aws-amplify/analytics provider exports and their RecordInput / ConfigureAutoTrack input types, and the prose and examples follow the existing web analytics pages in this repo. The mobile block is unchanged.

Validation

• yarn build passes; all 9 platform routes for pinpoint-migration prerender.
• Verified via the build output that the new content renders only for the 6 web/JS platforms and that the mobile platforms still render the original block, with no cross-contamination.
• Resolved all 1570 internal links on the 9 affected pages against the build output: 0 broken. Both new page links resolve on all 6 web platforms, and the in-page anchor to the Customer Profiles section is present on each.
• yarn spellcheck passes: 3023 files, 0 issues.
• MDX only, which .prettierignore excludes; no other files touched.

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