lisence: change the main lisence to AGPL-3.0

[MaojiaSheng]

Description

The OpenViking project uses different licenses for different components:

• Main Project: AGPLv3 - see the LICENSE file for details
• crates/ov_cli: Apache 2.0 - see the LICENSE for details
• examples: Apache 2.0 - see the LICENSE for details
• third_party: Respective original licenses of third-party projects

mentioned in #992

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1 out of 2 committers have signed the CLA.

✅ MaojiaSheng
❌ openviking

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[github-actions]

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