Replace bullet-list troubleshooting items with explicit level-3 headers
in README.md. No textual content was changed — only structure — to
improve Markdown parsing and avoid rendering/parsing errors on Ansible
Galaxy. This change makes the Troubleshooting section easier for
automated parsers to consume.

Signed-off-by: Colin Wilk <colin@wilk.cx>

Introduces a new 'yaml' strategy using Ansible's `from_yaml` to read
target files. This allows users to group multiple targets with
distinct label sets (e.g., severity or job) within a single file,
optimizing Prometheus file-based service discovery.

- Refactored task structure into `strategy_*.yml` for consistency.
- Extracted shared exporter variable computation.
- Implemented label merging where exporter labels override defaults.
- Included support for groups and hosts without labels to prevent crashes.

PR: (#1) https://github.com/kliwniloc/ansible-role-prometheus-target/pull/1

This added information about the possible ssh-server overloading and
run_once locking issues.

Signed-off-by: Colin Wilk <colin.wilk@tum.de>

This adds the run_once option for the two handler types (shell and
command). The variables `prometheus_target_handler_command_run_once`
and `prometheus_target_handler_shell_run_once` are introduced to
control this behavior.

For this change a switch from the Ansible Handlers to regular tasks was
necessary to  enforce run_once behavior with delegated hosts. If you
don't rely on handler specific features such as deferring, nothing
changes when using the role.

Signed-off-by: Colin Wilk <colin.wilk@tum.de>

The id property of the exporter is used for checking the default values
specified in `prometheus_target_exporter_defaults` variable.
However when both the `host` and the `path` fields are specified
manually in the `prometheus_target_exporter` list this id is never
looked up.
The way the templating was handled however, still resulted in an error
when leaving out the id field.
The templating code was now rewritten to allow for the following
exporter configuraion to run:

prometheus_target_exporter:
- { host: exporter_without_id, path: /opt/simple_target4.yml }

Signed-off-by: Colin Wilk <colin.wilk@tum.de>