Localstack Support: add way to change an AWS endpoint to custom

[ddemin]

Problem

• no any way to use this plugin in case of Localstack environment (instead of real AWS)

Solution

• add a new parameter called aws_endpoint_custom
• • real AWS integration will be used if this parameter has empty value (by default)
• • custom (e.g. Localstack) endpoint will be used instead of real AWS if you will use some URL as value for this parameter

[ddemin]

@JoseLuisSR please take a look, thanks!