Chore: Deprecate advanced search migrations (1 of 3)

What does this MR do and why?

• Part 1: 👉 this MR
• Part 1.a: !119969 (merged)
• Part 2: !118557 (closed)
• Part 3: !118558 (merged)

Deprecated migrations with failing specs split into separate MRs:

• !118628 (merged)
• !118633 (merged)

Resolves: #385424 (closed)

Related to: gitlab-org/search-team/migration-graveyard!1 (merged)

For future reference, I used this script to find which specs to update after marking migrations as obsolete.

#!/usr/bin/env bash

for filename in $(grep -Ril MigrationObsolete ee/elastic/migrate); do
    migration_name=$(echo $filename | cut -d '_' -f 2- | cut -d '.' -f 1)
    echo "#> $migration_name"
    grep -Rin ":$migration_name" ee/
done

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