Make default agents executable tested examples

[jezekra1]

We want to start creating more isolated "example agents" which would each showcase certain features, for example:

• working with files
• specific extension - e.g. request form
• storing conversation history
• etc...

Goal:

• Each example agent should be as simple as possible only showcasing a single feature.
• We can directly link or include the examples in documentation
• Examples should be in a top-level folder easily discoverable, not buried in tests
• The examples are tested to be working

Notes:

• The tests will require a running platform - the simplest solution is to add them to the integration or e2e test suites which both already spin up the platform in CI.
• E2E and integration tests already contain some test agents - see history_agent for inspiration
• See test_examples in beeai-framework as inspiration.
• Adding a new example agent should be scalable - for example adding a new agent should not make the tests run 30s longer due to a docker build, consider:
  • running agents directly from code (forbid extra dependencies in examples or add their dependencies as dev-dependencies)
  • building a single docker image for all agents
  • running agents without docker using uv subprocess

Example example:
/example_agents/extensions/form.py:
contains refactored form agent - https://github.com/i-am-bee/agentstack/blob/main/agents/form/src/form/agent.py#L28