Add tablets support

[amnonh]

Fixes #2119

[amnonh]

[mykaul]

The top is a bit ugly :-/
It is also inconsistent with the bottom, which has the nodes on the X axis. I'm also unsure - why are there no tablets at all @ 14:40 for example? Why does 10.4.9.133 suddenly has many a bit after 15:00?

[mykaul]

CC @bhalevy for awareness.

[bhalevy]

The top is a bit ugly :-/ It is also inconsistent with the bottom, which has the nodes on the X axis. I'm also unsure - why are there no tablets at all @ 14:40 for example? Why does 10.4.9.133 suddenly has many a bit after 15:00?

I would guess it show migrations.
I think a line graph of migrations rate would make more sense and then we can show it by DC/node/shard/whatever.

That said, we would probably need something similar for tablet replica rebuilds if they would be counted separately.
Cc @tgrabiec @dani-tweig

[tzach]

Can we try Tablets node as a simple line chart? maybe it will present the data better.

Migration is also a good idea, deserved its own panel(s).