Split the Aiven dictionary to separate out "business nouns"

[TibsAtWork]

At the moment, we have one Aiven dictionary for use in our linting, .github/vale/dicts/Aiven.dic. This includes words that aren't in the default dictionary, and also "business nouns" - company names, major products and so on.

I'd like to split the "business nouns" out to a separate dictionary, for a variety of reasons:

• They're not really the same thing as "ordinary words"
• Having them in a separate file would make it easier to scan for when we stop using one (some of them are referenced in one doc file only)
• I would like to automatically generate rules for catching mistakes in capitalising them. At the moment, the file .github/vale/styles/Aiven/common_replacements.yml has such rules for some names (for instance, datadog -> Datadog and clickhouse -> ClickHouse) but not for others (for instance, GitHub). Having a separate file would make it easy to (periodically) generate a companion style file for just this purpose. (For the GitHub example, if you instead use github, you just get told that word isn't recognised, which is not particularly helpful, but adding every word we want to catch like that, by hand, is onerous) [Note: see https://github.com/aiven/devportal/issues/1127 for an issue to address this]