fix: incorrect Java SDK installation and initialization code examples

[SaptarshiSarkar12]

Thanks for submitting a PR! Please check the boxes below:

• I have added information to docs/ if required so people know about the feature!
• I have filled in the "Changes" section below?
• I have filled in the "How did you test this code" section below?
• I have used a Conventional Commit title for this Pull Request

Changes

This PR fixes #4593 and brings the following changes 👇

• Added closing bracket to version xml tag and made changes to include </dependency> as a part of the code example, in installing the sdk section
• Updated the version of maven and gradle dependencies from 5.0.0 to 7.4.1
• Changed the builder method to newBuilder() under FlagsmithConfig class
• Formatted the maven dependency code with tabs (4 spaces) to look clean and good

How did you test this code?

1. Navigate to frontend directory.
2. Run npm ci
3. Run npm run dev
4. Open http://localhost:8080/ and create a test account.
5. Create a project after creating the organization.
6. Click on Environment section and then features from the side bar.
7. Checked the modified code examples by clicking in each of the two accordions.

[vercel]

@SaptarshiSarkar12 is attempting to deploy a commit to the Flagsmith Team on Vercel.

A member of the Team first needs to authorize it.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

2 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
docs	⬜️ Ignored (Inspect)	Visit Preview		Sep 9, 2024 3:57pm
flagsmith-frontend-preview	⬜️ Ignored (Inspect)			Sep 9, 2024 3:57pm

[github-actions]

Uffizzi Preview deployment-56036 was deleted.

[matthewelwell]

Thanks @SaptarshiSarkar12 !

[SaptarshiSarkar12]

Thank you @matthewelwell for reviewing and merging my PR ❤️!