Remove downgrade reference in agent_upgrade binary

[Rebits]

Wazuh version	Component
4.4	Agent Upgrade

Description

Agent downgrade is not officially supported. However, the agent_upgrade binary -F option, states the following:

Allows reinstalling the same version and downgrading the version.

This could lead to confusion among users, potentially resulting in the creation of unstable environments.
For this reason we should remove any reference to downgrade in the binary and documentation

[GGP1]

Update

Corrected the command help message and documentation to go in line with what the agent upgrade module documentation states.

Pull requests

wazuh: #18432
wazuh-documentation: wazuh/wazuh-documentation#6345

[GGP1]

Update

Rebased both related branches to 4.5.3.

[GGP1]

Update

Rebased branch again to re-run the checks and attached the execution of the framework unit tests to the PR description.