Introduce TOML-based configuration to replace data.py - #491

To make easier editing within our editors.
This format is compatible with multiple toml lsp, including taplo.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

Configuration is now done in config.toml and config.*.toml

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

Config files can now reference other TOML files via a root-level
`include` array.  Included files are deep-merged before the
including file's own content, with paths resolved relative to
the including file's directory.  Cycle detection prevents infinite
recursion.  Both `config.toml` and `config.{name}.toml` override
files support this mechanism.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

Configuration values can now be overridden at runtime with
`XCPNG_TESTS_`-prefixed environment variables.
Double underscores separate path segments (e.g.
`XCPNG_TESTS_network__free_nics='["eth1"]'` overrides
`config.network.free_nics`).

Values are parsed as TOML when possible, falling back to
plain strings - so booleans, integers, arrays, and inline
tables work naturally alongside plain string values.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

The config file now holds the inventory: [default] provides default
repositories/hosting_pool settings applied to all hosts, [hosts] lists
the pool masters to run against, and both pytest and tools.py read from
it. --config/-c accepts a profile name or a .toml file path anywhere on
disk; config.local.toml is auto-merged when no override is given, and
include paths resolve relative to the including file first, then the repo
root.

- tools.py: -i/--inventory removed; -H still overrides, -e/-x/-P act as
  temporary overrides; clean/exec fall back to config hosts too
- conftest: hosts fixture uses config [hosts] when --hosts is empty
- host_data(): fall back to default user/password for bare [hosts] entries
- schema: overlays validate without required keys while typos stay flagged
  (additionalProperties: false); new [default] section
- update task: guard against an empty pool list
- config.toml, README: document the new layout

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

-c NAME / XCPNG_CONFIG=NAME now looks up config.NAME.toml in the directory
given by the XCPNG_CONFIG_DIR env var when it is set, then in the xcp-ng-tests
repository root. A value that matches a file is otherwise used as a path
relative to the current directory; the repository root and current directory
are no longer searched for profile names.

Documented in the README's configuration section.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

Allow selecting a config overlay via the XCPNG_CONFIG environment variable,
equivalent to the --config flag. Update docs and CLI help accordingly.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

…against the base

`tools.py dump-config` prints the final configuration (base config.toml +
layered includes + overrides) as TOML, or JSON with --json; the TOML output
is deterministically ordered and syntax-colored on TTYs (--color/--no-color
to force). dump-config and migrate-data-py now print only values that differ
from the base config.toml, with --all restoring the full config. The shared
helpers (remove_defaults, deep_dict_equal, _strip_password_hashes) live in
lib/config_dump, and load_config gains apply_value_overrides=False to compute
the base config without XCPNG_TESTS_* / --config-value overlays.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

--config-value KEY=VALUE overrides a single config value at runtime, with the
KEY being a dotted path (double quotes around segments that contain dots).
Values are parsed as TOML, so booleans, numbers, arrays and inline tables
work too. Precedence is config.toml < overlay < XCPNG_TESTS_* env vars <
--config-value. Wired into pytest (--config-value) and tools.py; the override
is applied before the password hash is computed, so default_password and
default_password_hash stay consistent.

Documented in the README's configuration section.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

diff-config CONFIG1 CONFIG2 prints a unified diff between two resolved
configs, ignoring password hashes; TOML by default, --json for JSON
representation. Exits 0 when the configs are identical, 1 otherwise.
Configs are loaded without value/env overrides so both sides are compared
on their own contents.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

Make jobs.py use the same configuration as pytest and tools.py: -c/--config,
XCPNG_CONFIG/XCPNG_CONFIG_DIR and --config-value are now accepted, and
jobs.py run falls back to the hosts defined in the config's [hosts] section
when no hosts are given explicitly. Documented in the README.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

A config written for a newer version of the project may contain keys this
version does not support. Load it anyway, dropping the unknown keys with a
warning instead of aborting, so the same config can be shared across project
versions.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>