[19.0][MIG] pos_payment_method_change_policy: Migration to 19.0

[vasanthr-cp]

Description

This PR migrates the module pos_payment_method_change_policy to Odoo 19.0.

Changes Made

• Manifest: Updated version to 19.0.1.0.0.
• Documentation: Cleaned up documentation fragments (removed redundant .rst files in favor of .md).
• Packaging: Generated pyproject.toml using whool as per the latest OCA standards.
• Code: Verified compatibility with the Odoo 19 POS API.

Testing/Validation

• Ran pre-commit run --all-files locally and all checks passed.
• The module installs correctly in an Odoo 19 environment.

CC: @OCA/pos-maintainers

[pedrobaeza]

Thanks for the contribution.

Please preserve commit history following technical method explained in https://github.com/OCA/maintainer-tools/wiki/Migration-to-version-19.0.

If the jump is between several versions, you have to modify the source branch in the main command to accommodate it to this circumstance.

[vasanthr-cp]

"Hi team, just a friendly ping on this PR. All tests are passing and it's ready for review. Would appreciate any feedback!"

[cyrilmanuel]

LGTM

[vasanthr-cp]

@cyrilmanuel I've squashed all commits into one clean commit. Could you please re-approve?

[vasanthr-cp]

"Hi team, just a friendly ping on this PR. All tests are passing and it's ready for review. Would appreciate any feedback!"

@cyrilmanuel