Operations Repo Composability

# Purpose
Operations repos give an opportunity to configure sets of configurations across multiple IaC tools. Once you have a [catalog](https://github.com/bitovi/bitops/issues/321) (either your own set of ops repos/ops repo environments or a community provided set), it becomes easier to quick-start with stacks of configurations.
The problem even with a catalog is that users still need to copy configuration into their own ops repo environments.

This issue is to outline an approach to allow referencing external ops repos/ops repo environments rather than having to copy them directly.

# Implementation thoughts

Introduce a `bitops.config.yaml` at the environment level (which has other benefits as well) which has a block to the effect of:
```
default-environments:
- repo: https://github.com/bitops-operations-repos/kubernetes
environment: eks
version: 1.0.0
- repo: https://github.com/bitops-operations-repos/observability
environment: promStack
version: 1.2.0
- repo: https://github.com/bitops-operations-repos/observability
environment: grafanaStack
version: 1.1.0
- repo: https://github.com/bitops-operations-repos/k8s-ingress
environment: nginx
version: 1.0.0
- repo: https://github.com/bitops-operations-repos/k8s-service-mesh
environment: istio
version: 1.0.5
```
In this example, the deploy time execution of bitops against the environment in which this `bitops.config.yaml` is specified would first pull each of the external repos, then it would extract the specified `environment` contents, and then it would include the contents into the deployment configuration.

The above example would be sufficient to spin up an EKS cluster and add a prometheus stack (prom, node-exporter, alertmanager, etc), a grafana stack (grafana, loki, etc), an nginx ingress controller, and istio.

Obviously, much discussion should be had on exactly how these mechanisms work and what else can/should be specified.

The issue names no files, tests, or entry points. Start by reviewing the existing environment-level configuration and deploy-time execution flow, then resolve how external repositories, environments, versions, extraction, composition, and other configuration should work; done means an agreed design and an implemented, tested composability mechanism.

Written by the indexing model from the issue text.