Configure Spotless through common convention plugins

[gpunto]

Goal

AND-880

As the title says.

Note: I'm not running spotlessApply here to avoid bundling the migration with all the Spotless changes. I'll do it in a follow up (#26). What will change:

• The headers will add an empty line -> This is how chat & video were configured, so I used their template to minimize the overall changes, since core & feeds' codebases are smaller
• XML files now get the license header too

Implementation

Replace local Spotless configuration with the convention.

Testing

Run spotlessApply and verify that the files are updated accordingly.

Checklist

• Issue linked (if any)
• Tests/docs updated
• I have signed the Stream CLA (required for external contributors)

[github-actions]

PR checklist ✅

All required conditions are satisfied:

• Title length is OK (or ignored by label).
• At least one pr: label exists.
• Sections ### Goal, ### Implementation, and ### Testing are filled.

🎉 Great job! This PR is ready for review.

[Copilot]

Pull Request Overview

This PR migrates from the Spotless plugin to a centralized Stream conventions plugin (version 0.3.0), consolidating code formatting, license management, and Maven publishing configuration. This refactoring removes local configuration in favor of convention-based setup.

Key changes:

• Upgraded streamConventions from 0.2.0 to 0.3.0 and added stream-project plugin
• Removed Spotless plugin and migrated formatting configuration to streamProject extension
• Removed local license template files and license generation tasks

Reviewed Changes

Copilot reviewed 2 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
gradle/libs.versions.toml	Updated streamConventions version, added stream-project plugin, removed spotless plugin, fixed trailing space formatting
config/license/license.template	Removed license template file (moved to conventions plugin)
config/license/generated/license-2025.txt	Removed generated license file (moved to conventions plugin)
config/license/generated/license-2024.txt	Removed generated license file (moved to conventions plugin)
build.gradle.kts	Removed Spotless configuration, license generation tasks, and Maven publish configuration; added streamProject configuration block

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[gpunto]

@aleksandar-apostolov I'm not applying formatting here to avoid having all changes in the PR transitioning to the plugins. We can force merge this one and then merge the follow up: #26