Add Heroku log drain host format check

[andygout]

FTDCS-299

Jira card: https://financialtimes.atlassian.net/jira/software/c/projects/FTDCS/boards/1426?modal=detail&selectedIssue=FTDCS-299

Ref. Slack chat in which it was identified that the Heroku log drains for next-ads-api incorrectly prefixed its host param value with https:/ - Step 2.3 of the migration guide states that the host param value should be:

The Heroku app URL excluding the protocol and path (e.g. ft-next-article-eu.herokuapp.com)

References:

• Stack Overflow: javascript regular expression to not match a word
• Regular Expressions 101 (regular expressions tester)

[alexmuller]

Question: could we be more prescriptive here and require that it exactly matches the format ${process.env.HEROKU_APP_NAME}.herokuapp.com?

This environment variable is provided by the dyno metadata (https://devcenter.heroku.com/articles/dyno-metadata) which we know we need to have in order to get process.env.HEROKU_APP_ID.

[rowanmanning]

I forgot about that! I think that probs is a better shout, especially as we already have logic in place for validating that the environment variable is present. What a shame our beautiful RegExp isn't really needed 😄

[alexmuller]

Looks good, thanks!