Allow specifying the collectd_process_regex
Allow specifying the collectd_process_regex

Currently, in a few cases this is set incorrectly. One example is the
licensing frontend service, which uses a Procfile, but not gunicorn,
as the config class assumes.

Allow specifying this value manually, so that it can be corrected for
services where the required value differs from the default.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet