feat: update changelog to prep release

[hmalik88]

Summary

Adds a changelog entry to packages/site so the next release publishes a new site version aligned with @metamask/snap-simple-keyring-snap@2.1.0.

Why

The site embeds the snap's package.json version at build time:

// packages/site/src/utils/snap.ts
import snapPackageInfo from '../../../snap/package.json';
// ...
{ version: snapPackageInfo.version }

When v2.1.0 of the snap was released in #177, the release tool only bumped the snap package because only packages/snap/CHANGELOG.md had ## [Unreleased] entries. The site stayed at 2.0.1 on npm and still asks consumers to install snap v2.0.1 — which doesn't have the new keyring_setSelectedAccounts / keyring_resolveAccountAddress methods that @metamask/eth-snap-keyring@^22 now invokes.

This breaks the metamask-extension e2e suite for any flow that installs SSK via the companion site (create-snap-account, create-remove-account-snap, snap-account-contract-interaction, etc.) because the local site dependency resolves to v2.0.1 and the install never matches the v2.1.0 snap fixture.

Adding a ## [Unreleased] entry to packages/site/CHANGELOG.md makes the next release tool run bump and publish a new site version, while leaving the snap untouched (so no snap-registry allowlist update is required).

Changes

• packages/site/CHANGELOG.md: new ### Changed entry under ## [Unreleased] describing the bundled snap version reference bump.

Follow-ups

• Cut a patch release (e.g. 2.1.1) via the Create Release Pull Request workflow. The tool will bump and publish only the site; the snap stays at 2.1.0.
• In metamask-extension#42334, bump @metamask/snap-simple-keyring-site to the new version. No snap fixture changes are needed, the new site bundle still references snap v2.1.0.

---

Note

Low Risk
Documentation-only change in packages/site/CHANGELOG.md to trigger a site republish; no runtime or dependency code is modified.

Overview
Prepares the next @metamask/snap-simple-keyring-site release by adding an Unreleased changelog entry noting the bundled snap version reference bump from @metamask/snap-simple-keyring-snap@2.0.1 to 2.1.0, ensuring consumers install the updated snap via the dapp.

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