Support common annotation types

[gdlg]

Datumaro 2.0 shall provide support for the most common annotation types, including at least:

• Label
• Mask
• Polygon
• BBox
• Rotated BBox
• Keypoints

Future work

In the future (out of scope of this issue), we may add support for additional types, e.g.:

• Polyline
• Caption
• Cuboid2D
• Cuboid3D
• Super resolution
• Depth annotation
• Ellipse

And attributes such as:

• Object ID
• Group
• Z Order
• Arbitrary metadata

[leoll2]

Related PRs: #1834, #1868, #1877, #1880, #1894, #1895, #1927