[8.0] Refactor gfal2 and storageElement

[chaen]

(Replacement of #6127)

Although this PR has the potential to break things, I do not think it will. If you were in a situation that would break, it means:

• you are doing very advanced things with StorageElements, and you would recognize it
• your very advanced things work by chance, and it was just waiting to break. So this will make it deterministic.

It contains 4 main changes:

• simple migration to pytest for the Test_StorageFactory and Test_Resources_GFAL2
• When two storage plugins provide the same protocol, give priority to the local one
• Make an explicit distinction between the pluginName (which is the effectively used object to perform operations) and the protocolSectionName (which is the name of the section in the CS used to configure a given protocol).
• The DefaultProtocols option in the StorageElements section of the CS is unused anymore by GFAL2_SRM2 as redundant with outputProtocols

Historically, we never really had to deal with such cases, but now we have situations where the same storage plugin can be used for different protocols, and hence corresponds to two different protocol sections. We thus need to be able to make the difference.

It contains an API change for the StorageElement object (that will go in the wiki):

• se.storages was a list, it is now a dict. The keys are the protocol section name
• se.localPlugins becomes se.localProtocolSections
• se.remotePlugins becomes se.remoteProtocolSections
• se.getPlugins() becomes se.getProtocolSections
• se.getRemotePlugins() becomes se.getRemoteProtocolSections()
• se.getLocalPlugins() becomes se.getLocalProtocolSections()
• se.getStorageParameters: plugin parameter is replaced with protocolSection

In a second stage, I will tackle #4744 once for all

BEGINRELEASENOTES

*Resources

CHANGE: GFA2_SRM2 does not use anymore StorageElements/DefaultProtocols option in the CS (relies on specific OutputProtocols config)
CHANGE: explicit distinction between PluginName and ProtocolSection name in all the StorageElement components
CHANGE: API change for the StorageElement. See #6283 for details
CHANGE: StorageElement favors local plugins

ENDRELEASENOTES

[andresailer]

Maybe this is also a chance to update the Resources/StorageElement documentation section.
Also this comment #6127 (comment) ?

[andresailer]

Looks good to me, maybe some documentation updates are needed though

[chaen]

Thanks, I'll check Federico's review that I missed. And I will go over the StorageElement documentation. I will need another PR anyway

[chaen]

OK, I've updated the documentation and applied Federico's comment.
I think this is ready to go as is. I will most probably come up with another PR for continuing that revamp work