feat: enhance Broker HA mode docs

[shuaibmunshi]

Enchances the Snyk Broker documentation surrounding High Availability (HA) mode to provide better gudiance for running multiple instances of the Broker Client and adding an example Docker Compose file for deployments

High Availability Mode documentation updates:

• Clarified that high availability mode is enabled by default, supportng up to four Broker client replicas (deployment-tips-and-reference-architectures.md)
• Updated description to recommended Docker Compose for running multiple replicas, and removed instructions for enabling HA mode via environment variables or Helm arguments. (high-availability-mode.md)
• Improved explanation of required settings, emphasising that all Broker clients in an HA set must share the same BROKER_CLIENT_URL and BROKER_TOKEN. (high-availability-mode.md)

Prerequisites and deployment guidance:

• Changed prerequisites to recommend Docker Compose installation and configuration, instead of just Docker, and clarified environment variable naming. (prerequisites-for-universal-broker.md)

Running the Universal Broker client:

• Added a detailed section on running the Broker client and guidance for Helm deployments. (running-your-universal-broker-client.md)

[snyk-io]

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