Implement Admin Trends API

[andregasser]

Mastodon's Admin Trends API allows an admin to view trending links, statuses and tags. The goal of this task is to implement the following endpoints of this API in BigBone:

• View trending links
• View trending statuses
• View trending tags

The Admin Reports API as it is documented by Mastodon can be found here:
https://docs.joinmastodon.org/methods/admin/trends/

Tip: A lot of other endpoints similar to this have already been implemented. In order to get an idea how to implement this, I suggest that you study the code upfront. Start with one of the *Methods.kt files.

Please consult the following documents to make sure your contribution meets our projects criteria:

• Code of Conduct
• Code Contribution Guidelines

[andregasser]

Please do not start implementing this issue before #297 is merged into master, as some base entities will be created in the other story that are needed here as well (e.g. Trend::Link).