add: caching for Discovery Client

[VanillaSpoon]

Issue link

closes https://github.com/project-codeflare/multi-cluster-app-dispatcher/issues/611

What changes have been made

Adding a Discovery Client cache, which will reduce the calls to the Discovery Client, and prevent throttling. The cache is then refreshed by a ticker every 5 hours.

Checks

• [ ] I've made sure the tests are passing.
• Testing Strategy
  • [ ] Unit tests
  • [ ] Manual tests
  • [ ] Testing is not required for this change

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[VanillaSpoon]

Hey @KPostOffice, I believe mem cache would offer less latency between the discovery cache retrievals, as it appears to be the Discovery Api is used quite frequently. However, there may be other drawbacks to using the mem cache, so I'm open to suggestions/discussions on the topic :)

[KPostOffice]

@VanillaSpoon I'm unclear on exactly how the disk cache works if I'm being honest, because as part of the struct it wraps the memcache which makes me think that most requests will still go through the memcache.