doc: Updates to Frequencies by Country: Ecuador and LoRa Alliance link.

[ticlatam]

1. Added LoRa Alliance Frequency Parameters link
2. Updated Ecuador's frequency plan.

Summary

Closes #552
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Screenshots

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Changes

• LoRa Alliance Frequency Parameters link.
• Replaced US902-928 for AU915-928 for Ecuador.

Notes for Reviewers

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Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Run Locally: Verified that the docs build using make server, posted screenshots, verified external links.
• Style Guidelines: Documentation obeys style guidelines in CONTRIBUTING.
• Commits: Commit messages follow guidelines in CONTRIBUTING, there are no fixup commits left.

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