[1/5] Rename `throttle_unauthenticated_*` attributes in application settings API

What does this MR do?

In preparation for adding new rate limits for unauthenticated API requests, we add _web_ to the attributes for the current general unauthenticated rate limits in the application settings API:

• throttle_unauthenticated(_web)_enabled
• throttle_unauthenticated(_web)_period_in_seconds
• throttle_unauthenticated(_web)_requests_per_period

The API is changed to accept and return both the old and new names.

We'll rename the actual DB columns in a future issue, see #340031 for details.

Also see the previous MR !69379 (closed) where we attempted to rename the columns.

Issue: #335300 (closed)

Roadmap

1. Rename attributes for unauthenticated rate limit: 👈 This MR
2. Add columns for unauthenticated API rate limit: !69384 (merged)
3. Apply unauthenticated API rate limit in Rack Attack configuration: !69388 (merged)
4. Update settings form in admin area: !69486 (merged)
5. Documentation update: !69487 (merged)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• [-] I have added/updated documentation, or it's not needed. (Is documentation required?)
• [-] I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• [-] I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• 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.

Related to #335300 (closed)