Add support for BPM

[NouemanKHAL]

What does this PR do?

Adds support for using BPM instead of monit to manage the datadog agent processes in the BOSH release via the property bpm.enabled.
As a side effect, using BPM allows the Process Check to correctly collect both BPM and monit processes.

Description of the Change

• Add a feature flag bpm.enabled to control whether or not to use BPM.
• Add a template bpm.yml.erb to generate the BPM config bpm.yml which contains the configuration for the 4 agent processes (datadog-agent, process-agent, trace-agent, system-probe).
• Add spec properties to the dd-agent job in the form bpm.<PROCESS>.<LIMIT> to give control over each process limits (memory, open_files, processes).

Resources:

• BPM Configuration
• Migrating to BPM

Verification Process

Deployed on multiple testing environments (TAS 3.0, TAS 4.0).

Additional Notes

Release Notes

Review checklist (to be filled by reviewers)

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