add API for getting application terms of use

[pdurbin]

What this PR does / why we need it:

Client apps such as the SPA need to be able to retrieve the terms we present to users at signup.

Which issue(s) this PR closes:

• Closes Feature Request: Add API endpoint for obtaining Installation Terms Of Use #11415

Special notes for your reviewer:

It's sort of annoying that we call it :ApplicationTermsOfUse in the database but "General Terms of Use" in the UI. 🤷

I followed this: https://guides.dataverse.org/en/6.6/developers/api-design.html#exposing-settings (from #9890).

I'm aware that to PUT we use /lang/fr but to GET I used &lang=fr because it felt more natural. The PUT side was added in #6042.

I made an effort to make the entry in /openapi useful. Here's how it looks:

/info/applicationTermsOfUse:
  get:
    tags:
    - info
    operationId: Info_getApplicationTermsOfUse
    parameters:
    - name: lang
      in: query
      description: Two-character language code.
      required: false
      schema:
        type: string
      example: en
    responses:
      "200":
        description: Application Terms of Use (General Terms of Use) that must be
          agreed to at signup.

I cleaned up existing docs, including changing "Supported HTML Fields" to "Supported HTML Tags" while I was in there.

Suggestions on how to test this:

Try it with and without internationalization configured. Not that without the "lang" column in the "setting" table isn't used.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

No.

Is there a release notes update needed for this change?:

Yes, added.

Additional documentation:

Included. Here's a good starting point: https://dataverse-guide--11422.org.readthedocs.build/en/11422/api/native-api.html#get-application-terms-of-use-general-terms-of-use

[coveralls]

coverage: 23.005% (-0.002%) from 23.007%
when pulling 26b9be7 on 11415-app-tou
into cd48216 on develop.

[github-actions]

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