Create functions to generate and write a contributing teams table, and use that table in `write_webtext()`

[dylanhmorris]

Not for this PR, but in the spirit of https://github.com/CDCgov/hubhelpr/pull/38/changes#r2611588659 I think we could consider having this table be one of the datafiles generated in the reports directory in "step one" and then read it in here. That would allow us to remove base_hub_path as an argument to generate_webtext_block and write_webtext.

Originally posted by @dylanhmorris in #38 (comment)