Move DatastoreIO to separate project

[regadas]

Closes #3231

[codecov]

Codecov Report

Merging #3233 into master will decrease coverage by 2.61%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3233      +/-   ##
==========================================
- Coverage   72.95%   70.33%   -2.62%     
==========================================
  Files         232      234       +2     
  Lines        7639     7643       +4     
  Branches      331      342      +11     
==========================================
- Hits         5573     5376     -197     
- Misses       2066     2267     +201     

Impacted Files	Coverage Δ
.../src/main/scala/com/spotify/scio/ScioContext.scala	85.33% <ø> (-0.06%)	⬇️
...in/scala/com/spotify/scio/values/SCollection.scala	92.27% <ø> (-0.03%)	⬇️
...scala/com/spotify/scio/datastore/DatastoreIO.scala	12.50% <ø> (ø)
...tify/scio/datastore/syntax/SCollectionSyntax.scala	100.00% <100.00%> (ø)
...tify/scio/datastore/syntax/ScioContextSyntax.scala	100.00% <100.00%> (ø)
...scala/com/spotify/scio/bigquery/client/Cache.scala	0.00% <0.00%> (-74.08%)	⬇️
.../spotify/scio/bigquery/client/BigQueryConfig.scala	0.00% <0.00%> (-70.59%)	⬇️
.../spotify/scio/bigquery/BigQueryPartitionUtil.scala	0.00% <0.00%> (-52.50%)	⬇️
...scala/com/spotify/scio/bigquery/BigQueryUtil.scala	50.00% <0.00%> (-50.00%)	⬇️
...otify/scio/bigquery/syntax/ScioContextSyntax.scala	19.35% <0.00%> (-41.94%)	⬇️
... and 12 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e71a333...8f48a41. Read the comment docs.

[jto]

Given that it's a breaking change, I'd like someone else to also have a look before we merge it. Ping @nevillelyh @clairemcginty @syodage /

[regadas]

Hi @jto. I'm leaning towards not merging this. After thinking about this and #3234 I realised that this is not giving us what we really want and I started exploring this idea #3237 instead. wdyt?