Use arrow wheels to include arrow as a dependency in Ray

[pcmoritz]

At the moment we are compiling a fixed version of arrow as part of Ray (see

ray/cmake/Modules/ArrowExternalProject.cmake

Line 21 in 658c142

set(arrow_TAG b4f7ed6d6ed5cdb6dd136bac3181a438f35c8ea0)

). To

• improve build times,
• share more release infrastructure with arrow and
• make it easier for companies who package library dependencies separately to deploy Ray,

it makes sense to include arrow into Ray via pre-built packages. Because both Ray and arrow are fast moving, this will probably need nightly arrow releases (see also https://github.com/kszucs/arrow/blob/420886bea341af43743bf7c822aeec768abd9ae7/dev/tasks/nightlies.sample.yml).

[robertnishihara]

Done