Start process via actinia_module endpoint

[mmacata]

This PR allows to start a process via actinia_module endpoint.

• new HTTP POST endpoint /actinia_modules/<actiniamodule>/process
• only ephemeral processing is allowed for now
• the project is read from the actinia_module. Example template:

{
	"id": "ndvi",
	"description": "Generate NDVI map",
	"projects": ["nc_spm_08"],
	"template": {
...

in the future, multiple projects can be added comma separated to indicate for which project the process chain template can be used. For now the project to run the process in will be read from the template, so only one project should be defined.

• the schema for the HTTP POST body is not yet defined. It might be close to OGC API Processes. Right now, only a single value can be passed in the HTTP POST body without parameter name. It will then be checked for variable names inside the template and if only one is given, it will be used. If multiple variables are needed, this is not yet implemented as no schema is defined.
• the template is loaded, the one value from the request body is filled and the process chain is passed to actinia-core for processing.
• Response is the usual actinia-core response for processes containing resource_id which can be polled.

[linakrisztian]

Very nice, also to have the tests. Just some very minor comments.