Refactor admin search switch/case block

[gl2748]

maybe refactor to use a general json filter handler & apply this handler to the fingerprint and metadata fields -- we'll have to do some error handling maybe, though
and
Ben:
Regarding all the cases starting here https://github.com/steemit/faucet/pull/364/files#diff-c3a36f0b10b2fd1722b9c20199e08e35R82 what do you think about having a general handler for json nested property filters, and just letting the user input any path they want for json column filters? (this includes the actions.metadata, users.fingerprint, and users.metadata cols as of now) a reusable handler would save quite a bit of code & can be applied for at least the users.metadata field immediately

Iain:

yes that makes sense.

            ```case 'fingerprint':
                andList.push({
                    fingerprint: where(
                        literal("fingerprint -> `$${some_user_input}`),
                        { [nRegexp]: value }
                    ),
                });
                break;```

where ${some_user_input} would be whatever they put after 'fingerprint'
ditto for metadata.
not looked at actions.