[DOC] mockup for estimator overview table, for discussion

[fkiraly]

This issue is for defining and designing a mockup of the upgraded estimator overview.

I've tried to mock something up quickly (please ignore the colour scheme, this is just from copy-pasting and not having access to a commercial mockup tool):

Behaviour:

• the search table does a substring search, and subsets rows as in the current table.
• the dropdown, when selected, allows to select object type - optimally, any in the scitype register (not hard coded by the table). When selected, it subsets to that object type. This is and combination with the search.
• the tags checkboxes allow to select which tags are displayed. Only user-facing tags should be listed here, this can be queried using the user-facing tag, of the tag (yes, tags have tags). Or, there might be a small "show developer tags" buttin which extends the lits.
• the table is sortable and subsettable via the arrow symbols. The up/down arrow symbol is for sorting, like on Wikipedia. The dropdown arrow opens a list with all unique values, and subsets rows for objects with that value. (for value-or-list-of, it subsets to estimators whose lists contain the value)

[fkiraly]

Related: #6147