add AWS sigv4 support

[penghuo]

Description

1. add usage example. https://github.com/penghuo/os-sql/blob/flint-sigv4-pr/flint/docs/index.md#flint-datasource-readwrite
2. verified in using AWS EMR and AWS OpenSearch
   2.1. switch to Java 11
   by default, EMR using Java 8. Flint Spark is compiled using Java 11.

sudo alternatives --config java

2.2 mapping emr service role in FGAC
mapping AWS service role to FGAC role in AOS security. for example, mapping arn:aws:iam::xxx:role/service-role/AmazonEMR-InstanceProfile-yyy to all_access Roles in AOS Security

2.3 test read AWS OpenSearch data

import org.apache.spark.sql.SQLContext
import org.apache.spark.sql.SQLContext._
import org.apache.spark.sql._
import org.apache.spark.sql.types._

val aos = Map("host" -> "search-mytest-00001-xxx.us-west-2.es.amazonaws.com", "port" -> "-1", "scheme" -> "https", "auth" -> "sigv4", "region" -> "us-west-2")

val sql = new SQLContext(sc)
val df = sql.read.format("flint").options(aos).schema("aInt int").load("t001")

3. Remove scoverage plugin
   The scoverage plugin adds instrumentation code to scala source code to measure test coverage. when creating an assembly, we don't want to include this instrumentation code.
   Ignore scoverage plugin for now, will add it back later.

Issues Resolved

n/a

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #1663 (5f8a033) into feature/flint (56e6520) will not change coverage.
The diff coverage is n/a.

@@               Coverage Diff                @@
##             feature/flint    #1663   +/-   ##
================================================
  Coverage            97.19%   97.19%           
  Complexity            4107     4107           
================================================
  Files                  371      371           
  Lines                10464    10464           
  Branches               706      706           
================================================
  Hits                 10170    10170           
  Misses                 287      287           
  Partials                 7        7           

Flag	Coverage Δ
sql-engine	97.19% <ø> (ø)

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[dai-chen]

Thanks for the changes!