feat: support for parameters without slashes

[kefi550]

Currently, parameters structured with slashes, such as /some/parameter, can be successfully retrieved using the get_parameters_by_path API. However, when attempting to retrieve parameters that are not structured with slashes, such as some-parameter, the following error occurs when using get_parameters_by_path, leading to failure.

Received response status [FAILED] from custom resource. Message returned: Error: An error occurred (ValidationException) when calling the GetParametersByPath operation: The parameter doesn'
t meet the parameter name requirements. The parameter name must begin with a forward slash "/". It can't be prefixed with \"aws\" or \"ssm\" (case-insensitive). It must use only letters, nu
mbers, or the following symbols: . (period), - (hyphen), _ (underscore). Special characters are not allowed. All sub-paths, if specified, must use the forward slash symbol "/". Valid exampl
e: /get/parameters2-/by1./path0_.

This PR supports for handling non-hierarchical parameters (those without slashes) by incorporating the get_parameter API in addition to the existing get_parameters_by_path API. This allows retrieval of both hierarchical and non-hierarchical parameters.