Add configurable application setting for decompressed archive size limits

Problem

Currently, users can work around decompressed archive size limits when importing projects by enabling the validate_import_decompressed_archive_size which has been enabled by default in !63025 (merged).

The usage of the feature flag is documented in https://docs.gitlab.com/ee/security/project_import_decompressed_archive_size_limits.html.

Removing the feature flag will prevent users from working around this limitation.

Proposal

• Let's remove the feature flag validate_import_decompressed_archive_size
• In the UI, let's add an application setting under Admin Settings > General > Account and limit called Decompression ratio for imported archives, which accepts an integer and is set to 2 by default.
• We also need to update https://docs.gitlab.com/ee/user/gitlab_com/#account-and-limit-settings by adding the default value for the newly introduced setting.
• We need to also update the application settings API along with the docs.
• Let's drop the page https://docs.gitlab.com/ee/security/project_import_decompressed_archive_size_limits.html following this process

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