In GitLab EE, a GitLab instance can be read-only (e.g. when it's a Geo
secondary node). But in GitLab CE it also might be useful to have the
"read-only" idea around. So port it back to GitLab CE.

Also having the principle of read-only in GitLab CE would hopefully
lead to less errors introduced, doing write operations when there
aren't allowed for read-only calls.

Closes gitlab-org/gitlab-ce#37534.

Improved file logging for authentication events

See merge request gitlab-org/gitlab-ce!9196

# This is the 1st commit message:
Add logging for all web authentication events

# This is the commit message #2:

Re-add underscore to after_inactive_sign_up_path_for

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Standardize on username=

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after_filter -> after_action, _resource -> resource

# This is the commit message #5:

Add two-factor login failures and account lockouts

# This is the commit message #6:

Move logging from two-factor concern to user model

# This is the commit message #7:

Add spaces around default parameter assignments

# This is the commit message #8:

Move logs out of user model

# This is the commit message #9:

Replace filtered_params with user_params

# This is the commit message #10:

Standardize case

# This is the commit message #1:

Fixes for username and AppLogger.info

This avoids loading the `OmniAuthCallbacksController` at boot time so
it doesn't mess up the `before_action`-chain