docs: update Flutter Web Example

[sashatalalasha]

Proposed changes

This PR installs new versions of dependencies, fixes Ory base URL used for Ory Proxy and updates the guide.

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
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[CLAassistant]

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[Benehiko]

Don't use the ory proxy for this please! I intentionally removed the proxy usage with the flutter example due to the test flakes. The proxy makes the flutter app significantly slower to load in the browser since it pushes all the flutter assets through the proxy! with the tunnel it's only serving Ory-related data and the flutter app is loaded directly from its own dev server.

[Benehiko]

As I have commented on the PR - we shouldn't use the Ory Proxy with the flutter example!

[Benehiko]

LGTM :)