issues with multiple tags separator for CMS files/pages

In provider portal navigate to Audience -> Content -> some file or page (e.g. mouse.jpg)

There you can see an empty `tag_list` field.

First issue is that user is not instructed what separator must be used when setting multiple tags (the correct separator is comma ",". If space " " is used, then the whole line is considered as a single tag)

If user enters tags with proper separator, e.g. "tag1,tag2,tag3" and saves the file, the page gets reloaded and the tags appear as "tag1 tag2 tag3". If this is then saved again, the tags of the file are stored as a single tag of "tag1 tag2 tag3". So if user edits some other property and does not touch tags at all, the tags will still be messed up.

For pages the issue is the same. But one has to reload the page manually or navigate away from page, then open it again (e.g. "Homepage") to see the tag separator being replaced by a space.

In existing tags I see that there are a number of tags that are mistakenly saved as a single tag. e.g. `card smartcard`, `aaa bbb ccc`, a number of them seem to be deliberately a single tag, e.g. `Red Hat`, and a number of them are not clear whether they are intentionally a single word or not.

So splitting on space doesn't seem like a viable option.

What we can probably do without any downsides is

• add a help message in the form for the user pointing out that multiple tags need to be separated by a comma
• when visualizing existing tags, properly join them by comma instead of a space

P.S. seems like forum posts tagging support has been removed with (https://github.com/3scale/system/commit/e85ab77508c)