Add columns for web_based_commit_signing_enabled group and application setting

What does this MR do and why?

Adds columns for cascading settings web_based_commit_signing_enabled at application and group level.

Migration Output

VERSION=20250416103445 bin/rails db:migrate:up:main

[advisory_lock_connection] object_id: 133860, pg_backend_pid: 38999
20250416103445 AddWebBasedCommitSigningEnabledSetting: migrating ===========
column_exists?(:namespace_settings, :web_based_commit_signing_enabled)
-> 0.0329s
column_exists?(:namespace_settings, :lock_web_based_commit_signing_enabled)
-> 0.0025s
column_exists?(:application_settings, :web_based_commit_signing_enabled)
-> 0.2054s
column_exists?(:application_settings, :lock_web_based_commit_signing_enabled)
-> 0.1954s
add_column(:namespace_settings, :web_based_commit_signing_enabled, :boolean, {:default=>nil, :null=>true})
-> 0.0019s
add_column(:namespace_settings, :lock_web_based_commit_signing_enabled, :boolean, {:default=>false, :null=>false})
-> 0.0020s
add_column(:application_settings, :web_based_commit_signing_enabled, :boolean, {:default=>false, :null=>false})
-> 0.0019s
add_column(:application_settings, :lock_web_based_commit_signing_enabled, :boolean, {:default=>false, :null=>false})
-> 0.0013s
20250416103445 AddWebBasedCommitSigningEnabledSetting: migrated (0.4481s) ==
[advisory_lock_connection] object_id: 133860, pg_backend_pid: 38999

VERSION=20250416103445 bin/rails db:migrate:down:main

[advisory_lock_connection] object_id: 138280, pg_backend_pid: 38772
20250416103445 AddWebBasedCommitSigningEnabledSetting: reverting ===========
column_exists?(:namespace_settings, :web_based_commit_signing_enabled)
-> 0.0348s
remove_column(:namespace_settings, :web_based_commit_signing_enabled)
-> 0.0022s
column_exists?(:namespace_settings, :lock_web_based_commit_signing_enabled)
-> 0.0021s
remove_column(:namespace_settings, :lock_web_based_commit_signing_enabled)
-> 0.0006s
column_exists?(:application_settings, :web_based_commit_signing_enabled)
-> 0.1902s
remove_column(:application_settings, :web_based_commit_signing_enabled)
-> 0.0020s
column_exists?(:application_settings, :lock_web_based_commit_signing_enabled)
-> 0.1861s
remove_column(:application_settings, :lock_web_based_commit_signing_enabled)
-> 0.0013s
20250416103445 AddWebBasedCommitSigningEnabledSetting: reverted (0.4237s) ==
[advisory_lock_connection] object_id: 138280, pg_backend_pid: 38772

References

Related to Add controls to allow groups to opt in to web-b... (#439980 - closed)
Work breakdown
Draft: [ci skip][DO NOT MERGE][PoC] cascading s... (!188452)

MR acceptance checklist

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