Remove mandatory "name" on editing process (agent, agent groups and datasets)

[manrodrigues]

Nowadays is not possible to make a PUT request to agents, agent groups and datasets endpoint without inform the name of the elements. However, as the name already exists, it should not be needed for the edit process.

Expected behavior:
PUT requests to /agents/id, agent_groups/id and /policies/dataset/id must NOT require "name" to be done.

• If the name is informed, the new name must overwritten the old name
• If the name is omitted, the old name must be maintained.
• If the name is informed with empty or invalid values, an error must be raised informing that the name doesn't match with the pattern required.

Originally posted by @manrodrigues in #2005 (comment)

[manrodrigues]

ok.. name is not required on editing process anymore