Provide ability to extend or overwrite cloud resource tags

[tleguijt]

Related to the following PR: #57

MACH sets resource tags by default (at least; in Azure for now).
It should be possible to either extend or overwrite them in MACH with an extra tags setting in your Site configuration.

I think being able to overwrite them gives you the most flexibility. I think we should not provide both options (overwrite and extend) because it will make the configuration more complex.

[MichielBijland]

maybe we can implement this in away that feels the same as AWS: #143

[mvantellingen]

We should be able to define tags on global level and site level and component level. Tags set on site level should be passed to the plugins so that for example aws can set default tags

[demeyerthom]

I think this first requires #244, so we can change the plugin protocol and allow for setting and handling tags