Improve RemoteName parser

[edigaryev]

OCI image names are widely used, but a formal spec on their format is missing. Here's what what OCI's Unique Resource Identifiers says on the subject, for example:

How do we ask for containers? We ask for a unique resource identifier (uri) which broadly comes in this form:

There's nothing formal in the entire document, except that the resource identifier is split into registry, organization and repository.

There's an implementation in Docker's distribution package, which is way more complicated than our's RemoteName parser.

There's an attempt to derive an EBNF grammar which is quite readable at first glance (compared to a bunch of regular expression above), so perhaps we should validate it and stick to it.

[edigaryev]

Here's an upstream PR that once merged, will allow us to bring back the new parser: antlr/antlr4#3906.