Separate basic security guidance from tenant token documentation

[guimachiavelli]

The security section has grown a bit and it's possible users can't parse the existing articles efficiently. One way to mitigate this would be to separate general security guidance (e.g. API and master keys) from specific topics that target more specific use cases (e.g. tenant tokens).

References

• Slack discussion (private link): https://meilisearch.slack.com/archives/C07CLB9J4BH/p1739268542410199