HAProxy supports the use of map files for selecting backends, or
a number of other functions. See [1] and [2].
This patch adds the key `maps` for each service definition allowing
fragments of a complete map to be defined across all the services,
with each service contributing some elements to the overall map file.
The service enabled/disabled and state flags are observed to add and
remove entries from the map file, and individual map entries can also
be marked as present/absent to make inclusion conditional.
[1] https://www.haproxy.com/blog/introduction-to-haproxy-maps/
[2] https://www.haproxy.com/documentation/hapee/latest/configuration/map-files/syntax/
Change-Id: I755c18a4d33ee69c42d68a50daa63614a2b2feb7
d548b7e5ff