GORA-276: Refactor and organize o.a.g.mapreduce package naming

[nbrendah]

Issue Link: https://issues.apache.org/jira/browse/GORA-276

Migrated classes in package org.apache.gora.mapreduce to org.apache.gora.io.serializer

cc @djkevincr

[nbrendah]

My PR is failing. @lewismc, what is the cause of

Going to parse results form **/*-reports/TEST-*.xml
Result: 1352 tests run, 29 skipped, 0 failed.
Posting status 'completed' with conclusion 'success' to https://github.com/apache/gora/pull/251 (sha: 07293dc17249838fb781c01ca624318f4b29917e)
Error: Resource not accessible by integration

[lewismc]

Yeah I saw that and I tried to fix it.
@djkevincr do you know when the Github Actions build started failing?
I did see actions/first-interaction#10 (comment)

[nbrendah]

Yeah I saw that and I tried to fix it.

@lewismc I saw your current commit 44ecabb . It was passing build, though failing with sonar scanners.
However, most of these builds pass locally.

[lewismc]

This is a real blast from the past @nbrendah
This patch introduces a major API break... so we need to think about how clients will address that.

[nbrendah]

Sorry @lewismc for taking long without replying to this. I was finishing my outreachy application

This patch introduces a major API break... so we need to think about how clients will address that.

@lewismc @djkevincr Should we create documentation to show this change or I close this because negative results outweigh the positive?

[nbrendah]

I had to send an empty commit to re-run the build.
I guess it passes and we continue with our discussion