Draft: Global search 15.0 breaking changes

What does this MR do and why?

This is a long-running branch that includes breaking changes associated with 15.0 release.

⚠ Note: this branch cannot be merged until 22nd April or later.

Changes will include:

• Updates ES client to 7.13.3, deprecates _type !79949 (merged)
• Removes user_email_lookup_limit !83356 (merged)
• Deprecate old advanced search migrations !83937 (merged)

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.