Remove deprecated SendGrid Legacy Marketing Campaigns functionality

[Copilot]

Description of change

SendGrid deprecated the Legacy Marketing Campaigns API (/v3/contactdb/*, /v3/campaigns endpoints) and removed the marketing_campaigns.read scope. Modern accounts lack this scope, causing authorization failures during discovery.

Changes:

• Removed marketing_campaigns.read from required scopes in streams.py
• Removed deprecated streams: contacts, lists_all, lists_members, segments_all, segments_members, campaigns
• Retained supported streams: suppression management (global_suppressions, invalids, bounces, blocks, spam_reports), suppression groups (groups_all, groups_members), and templates (templates_all)
• Updated README to document removed functionality

Authorization check remains in place, now validates only current scopes: suppression.read, asm.groups.read, templates.read, templates.versions.read.

Manual QA steps

• Run discovery with a modern SendGrid account
• Verify authorization check passes without marketing_campaigns.read scope
• Verify only supported streams appear in catalog

Risks

• Users relying on deprecated streams (contacts, lists, segments, campaigns) will no longer have access to them
• Existing state files referencing deprecated streams will need to be updated

Rollback steps

• revert this branch

AI generated code

https://internal.qlik.dev/general/ways-of-working/code-reviews/#guidelines-for-ai-generated-code

• this PR has been written with the help of GitHub Copilot or another generative AI tool

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