create intake source for experiment table

[ryanSoley]

Is your enhancement request related to a problem? Please describe

we would like to be able to share visualizations alongside the projects and experiments in the intake catalogs. for example, catalog.read() returns projects and experiments. we'd like to ultimately have something like catalog.serve() that mimics the viz module's serve functionality to launch a dashboard with the experiments returned by catalog.read()

in #441 we created a base source for visualizations. we will need a concrete implementation for each visualization, like we have for experiments. this issue will track the creation of a source for the experiments table

Describe the solution you'd like

add a new ExperimentsTableDataSource that extends VizDataSourceMixin. the __init__ function should take in any additional arguments specific to the ExperimentsTable. _get_schema should create a visualization and set it as the _visualization attribute, as well as update the metadata with any required attributes

Additional context

at this point, the visualization stored in _visualization does not need to have any experiments in it - we'll get to that later

[ryanSoley]

closed w/ #456