Add 'axis' option for 'tf.boolean_mask()' (#11558)

* Add 'axis' option for 'tf.boolean_mask()'

This fix tries to address 9721 where it was not possible to pass an
'axis' option for 'tf.boolean_mask()'.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add tests for 'axis' option in 'tf.boolean_mask()'

This fix adds tests for 'axis' option in 'tf.boolean_mask()'

This fix is part of the effort to fix 9721.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Move the new args 'axis=None' to the end for backward compatibility

This fix move the new args 'axis=None' to the end for backward compatibility
and adds additional tests to cover cases where mask is more than 1-D.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update docstring for 'tf.boolean_mask()'

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update goldens for api compatibility changes.

This commit update API goldens.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>