Parse TOML definition files to improve generated LookML

[ncalexan]

#391 implemented generating LookML dashboards for opmon projects. The implementation queries BQ and uses various heuristics to determine what the precise form of the dashboard should be. This is clearly not optimal: the underlying TOML files are the correct place for the user to configure the produced dashboard.

This ticket tracks parsing the appropriate TOML definition files to allow for customization of the produced dashboard.

For a first round of use cases, I would like to be able to:

• not see the percentile filter (Only show percentile filter if there are percentile stats opmon#84)
• allow to group dimensions and to select multiple dimensions simultaneously (Allow to group multiple dimensions into one dashboard in the same way that metrics can be grouped opmon#137)
• change the title and description of graphs

based on the TOML definitions.

┆Issue is synchronized with this Jira Task