identus-cloud-agent docs: add local stack examples

Description:

Open for feedback. Experiment with local examples with generated docker configurations.

https://nickel-lang.org/ is used to generate all compose.yaml in each example.

example	description
`st`	single-tenant configuration without external services (except database)
`st-multi`	3 instances of single-tenant configuration
`st-vault`	single-tenant with Vault for secret storage
`mt`	multi-tenant configuration using built-in IAM
`mt-keycloak`	multi-tenant configuration using Keycloak for IAM
`mt-keycloak-vault`	multi-tenant configuration using Keycloak and Vault

Example we might consider in the future

vault with file storage
vault with AppRole authentication
keycloak with agent admin role
oidc4vc configuration
overriding config with application.conf
production?

Checklist:

[ ] My PR follows the contribution guidelines of this project
[ ] My PR is free of third-party dependencies that don't comply with the Allowlist
[ ] I have commented my code, particularly in hard-to-understand areas
[ ] I have made corresponding changes to the documentation
[ ] I have added tests that prove my fix is effective or that my feature works
[ ] I have checked the PR title to follow the conventional commit specification

Mar 20 '24 14:03 patlo-iog

Integration Test Results

19 files ±0 19 suites ±0 3s :stopwatch: -1s 39 tests ±0 39 :white_check_mark: ±0 0 :zzz: ±0 0 :x: ±0 66 runs ±0 66 :white_check_mark: ±0 0 :zzz: ±0 0 :x: ±0

Results for commit 77c20d02. ± Comparison against base commit fe22d22d.

:recycle: This comment has been updated with latest results.