feat: Validate Collection memory config through adding conflictsWith validation

[MasonLegere]

Which problem is this PR solving?

Fixes #803 by ensuring that only both AvailableMemory and MaxAlloc cannot be set at the same. MaxMemoryPercentage may still be set regardless as it has a default value defined.

While making this changes I noticed that when only AvailableMemory was defined I ran into a validation requireWith error. The validation only fails on the first pass before defaults are loaded in from the config struct. If the failure is intentional then we probably should remove the default -- only breaking change I could see is if someone was running with validations turned off explicitly.

 $ docker-compose up
[+] Running 1/0
 ✔ Container refinery-refinery-1  Recreated                                                                   0.0s
Attaching to refinery-refinery-1
refinery-refinery-1  | 2023/07/24 07:57:40 maxprocs: Leaving GOMAXPROCS=6: CPU quota undefined
refinery-refinery-1  | Validation failed for config file /etc/refinery/config.yaml:
refinery-refinery-1  |   the group Collection includes AvailableMemory, which also requires MaxMemoryPercentage
refinery-refinery-1  |
refinery-refinery-1  |
refinery-refinery-1 exited with code 1
$ cat config.yaml 
General:
  ConfigurationVersion: 2
  MinRefineryVersion: v2.0


Collection:
  AvailableMemory: 2Gb

Short description of the changes

• Adds conflictsWith validation type acting in an opposite way to requireWith
• Modified requireWith to check whether or not the required field has a default value

Fixes #803.

[kentquirk]

This is good, thanks. Minor tweaks, please.