Context menu, tooltips, hints. Curved line & first color in plots / VS Code DVC

[maxagin]

Sharing some examples based on my and @mattseddon discussion + some other general improvements. If needed let's jump on call to discuss this changes.
Figma file

[maxagin]

@shcheklein please let me know if this is right way to create a task on GitHub. Thanks !

[mattseddon]

@maxagin

I rolled the context menus feedback in with #1603.

Rounded plots lines -> We cannot easily update plots to have rounded lines. IMO it would be better to leave the template as is. If we update the behaviour for Vega we would have to do the same thing for all of the upcoming plots providers as DVC starts to accommodate them as well. Having rounded lines for plots also runs against all of the straight edges shown in the rest of VS Code.

Using grey color as the default for plotting -> We are currently debating the behaviour of selecting revisions from the experiments table. The behaviour will be updated in #1607 but may change again based on the decisions in #1565 (see Toggling plots visibility concept). One thing to note is that currently whatever color we use for the dark theme will be reflected in the light theme. This is due to some limitations with the way that VS Code works.

Will close this one for now. LMK if I have missed anything.