Move policies index page into index folder

What does this MR do?

Move policies index page into index folder

• with !67929 (merged), the policies controller standardized its actions
• the webpack script started picking up ee/app/assets/javascripts/pages/projects/security/policies/index.js for all the policies actions due to that MR, so I updated the path to the file to be ee/app/assets/javascripts/pages/projects/security/policies/index/index.js
• I see the <controller_name>/index.js pattern in the code base, but only for paths that have only one action
• I see the <controller_name>/index/index.js pattern in the code base for controllers with more than one action

Related to #321884 (closed)

Screenshots or Screencasts (strongly suggested)

Page	Before	After
policies#index
policies#new

How to setup and validate locally (strongly suggested)

1. Navigate to a project
2. Navigate to Deployments => Environments and create an environment
3. Turn on the :security_policies_orchestration_configuration feature flag
4. Navigate to Security & Compliance => Policies => New policy

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team