* If it raise error `Azure::Core::Http::HTTPError`, return `nil` instead of `false` in
  `ActiveStorage::Service::AzureStorageService#delete`.

* Other services behave as same as this.

The `keyfile` was renamed to `credentials` in `google-cloud-storage` 1.8.0.
https://github.com/GoogleCloudPlatform/google-cloud-ruby/blob/master/google-cloud-storage/CHANGELOG.md#180--2017-11-14

Although `keyfile` can still be used, but it looks like deprecate.
https://github.com/GoogleCloudPlatform/google-cloud-ruby/blob/ddf7b2a856d676316525eb581c1a4cc83ca6097b/google-cloud-storage/lib/google/cloud/storage.rb#L589...L590

Therefore, I think that should use `credentials` in newly generated
applications.

Ref: https://github.com/GoogleCloudPlatform/google-cloud-ruby/issues/1802

Closes #31073.

Relying on the GET request issued first to fetch the file we want to
delete is not enough to avoid this error. If the file is deleted after
our GET request but before the DELETE request we'll get a NotFound error
that after all means that the file is already deleted, so it can be
safely ignored.

`content_type` parameter is before `disposition` parameter.

And enable `context_dependent` of Style/BracesAroundHashParameters cop.

Follow up of #30188.

* Use `+` instead of backquote.
* Remove escape from class to be link

Add in the content_type option, which is defined as part of the generic
ActiveStorage::Service class.

Without this option, attempts to generate a URL for an attached file
fail with "ArgumentError (unknown keyword: content_type)"

The reasons for this commit are:

- uniformity with the other Rails libraries
- (possibly) behave better with respect to autoloading
- fix the index in the generated documentation

Before this commit, run `rake rdoc` generates this left sidebar
(ActiveStorage entries are indexed twice, both inside and outside the module):

<img width="308" alt="before" src="https://user-images.githubusercontent.com/10076/28939523-7c087dec-7846-11e7-9289-38ed4a2930cd.png">

After this commit, run `rake rdoc` generates this left sidebar:
(ActiveStorage entries are only indexed inside the module):

<img width="303" alt="after" src="https://user-images.githubusercontent.com/10076/28939524-7c090be0-7846-11e7-8ee5-29dfecae548e.png">

We are already removing the braces around hash parameters in the last
argument in other places so we should not change the entire codebase
because of two places.