Support multiple templates in config entries

[glpatcern]

This PR introduces support for config entries with multiple templates, such as parameter = "{{ vars.v1 }} foo {{ vars.v2 }}".
Previously, only one {{ template }} was allowed in a given configuration entry.

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[glpatcern]

Not sure why integration tests fail, especially as the logs show 500 Internal Server errors. The specific test for configuration templates was extended and passes.

[gmgigi96]

@glpatcern Try to run it locally. You will have also the reva logs to understand why. Just type make [litmus-1|litmus-2|acceptance-2]

[glpatcern]

For the record, to be looked at:

The reva gateway panics in the litmus-1 scenario in storageprovider.go:1338, i.e.:

if etagIface, err := s.etagCache.Get(statRes.Info.Owner.OpaqueId + ":" + statRes.Info.Path); err == nil {

Relevant stack trace:

        /usr/local/go/src/runtime/panic.go:914 +0x21f
github.com/cs3org/reva/internal/grpc/services/gateway.(*svc).statHome(0xc000000f00, {0x172f008, 0xc0008afda0})
        /home/reva/internal/grpc/services/gateway/storageprovider.go:1338 +0x19b
github.com/cs3org/reva/internal/grpc/services/gateway.(*svc).Stat(0xc0008af8c0?, {0x172f008, 0xc0008afda0}, 0xc00071f860)
        /home/reva/internal/grpc/services/gateway/storageprovider.go:1500 +0xd70

[glpatcern]

Somehow surprisingly, fixing a flaw in the logic (a not found key should not be replaced) fixed all the scenarios.

The PR is ready for review.