Add caching

[tobiscr]

Description

Add caching for secrets and applications.

Related issue(s) https://github.com/kyma-project/application-connector-manager/issues/150

[koala7659]

Measurement results:

Hyperscaler: Azure Region: westeurope Landscape: kyma-dev

Gateway scaled to 1 replica:

• At 20 req / sec - 100% requests processed with no error with average latency 0.00393s.
• At 40 req / sec - 100% requests processed with no error with average latency 0.0065s.
• At 100 req / sec - 100% requests processed with no error with average latency 0.0133s.
• At 150 req / sec - 99% requests processed with no error with average latency 0.0160s. Success Count 149980 (99%) Failed Count: 20 (1%). At increased pod resources
• At 200 req / sec - 99% requests processed with no error with average latency 0.0207s
  Success Count 199940 (99%) Failed Count: 60 (1%). At Increased pod resources
• At 500 req / sec - 77% requests processed with no error with average latency 0.3906s Success Count 386429 (77%) 113571 (23%). CPU Saturation max 140% At increased pod resources

Gateway scaled to 5 replicas:

• At 500 req / sec all requests was processed with no error with average latency 0.0354s At increased pod resources

Increased pod resources

          limits:
            cpu: "1"
            memory: 512Mi
          requests:
            cpu: 20m
            memory: 256Mi 

The safe value for a load seems to be between 100 req /sec - 150 req /sec