docs: add agents.md file (#410)

*Issue #, if available:* n/a (ref
aws/aws-durable-execution-sdk-python#177)

*Description of changes:*
Proposal of an [AGENTS.md](https://agents.md/) file (Kiro
[compatible](https://kiro.dev/docs/steering/)) how to build and test
durable functions with coding agents with JavaScript or Python. Ideally,
this file lives in a shared repository.

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choice.

Signed-off-by: Michael Gasch <15986659+embano1@users.noreply.github.com>

Author: embano1