Token prefixes: Add support for oauth application secrets

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What does this MR do and why?

This MR adds support for instance wide token prefixes to oauth application secrets.

Instance wide token prefix have been added with !179852 (merged)

The new prefix format is: #{instance_prefix}#{token_type_prefix}. E.g. for incoming mail tokens, we'd get: #{instance_prefix}gloas-. By default, this is the current token prefix gloas-. However, we can now customize the instance prefix to create a new prefix: mycompanynamegloas-.

With this custom prefix, it is easier to identify leaked tokens, because we can now skip all leaked tokens that start with gloas. Now, we only need to look at tokens starting with mycompanynamegloas-.

🛠️ with ❤️ at Siemens

References

• Previous MR that adds support for Incoming email tokens
• Issue

How to set up and validate locally

1. Enable feature flag via rails c:

Feature.enable(:custom_prefix_for_all_token_types)

2. Generate a new application at https://gdk.test:3443/oauth/applications. Name can be anything, as an URL you can use http://localhost
3. Now, change the instance wide token prefix: Admin area > General > Account and limit > Instance token prefix, e.g. to mycustomprefix
4. Renew the token of the application. You should now see a new, prefixed token.

MR acceptance checklist

MR Checklist ( @nwittstruck)

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the javascript style guides
• Conforms to the database guides

Related to #388379