S3 credentials should be optional

[dgarus]

Close artipie/artipie#1281

• credentials are made optional for S3 storage factory; added test;
• added using S3 storage factory to get a storage instance in tests.

[olenagerasimova]

@dgarus thanks, also, I think, we need to update wiki by specifying that credentials in s3 config are optional and can be set in env variables.
And, as Config interface was changed, http has to be updated and this new method should be implemented.

[dgarus]

@dgarus thanks, also, I think, we need to update wiki by specifying that credentials in s3 config are optional and can be set in env variables. And, as Config interface was changed, http has to be updated and this new method should be implemented.

Yes, good point.
Thanks