SqlServerDsc: Documentation updates

[johlju]

Pull Request (PR) description

• SqlServerDsc
  • Remove the file .github/CONTRIBUTION.md as it no longer filled any
    purpose as GitHub will find the CONTRIBUTION.md in the root folder
    directly now (issue Move the CONTRIBUTING.md files together #1227).
  • The documentation in CONTRIBUTING.md has been somewhat updated.
  • Update documentation around design pattern for accounts that does not
    use passwords (issue SqlSetup: Does not allow null or empty password for MSA #378)
    and (issue SqlSetup: Add documentation around how to use built-in account #1230).
  • Updating the Integration Test README.md to better explain what the
    integration tests for SqlSetup, SqlRSSetup, and SqlRS does (issue Integration Tests: Contributing.md should be updated with the different test jobs #1315).
• SqlAGReplica
  • Update documentation with a requirement for SqlServer in certain circumstances
    (issue SqlAGReplica: InnerException: Invalid column name 'required_copies_to_commit' #1033).
• SqlRSSetup
  • There was a typo in the error message that was thrown when not passing
    either the Edition or ProductKey that could be misleading (issue SqlRSSetup: Document that the properties ProductKey and Edition is mutually exclusive  #1386).
  • Updated the parameter descriptions for the parameters Edition and
    ProductKey that they are mutually exclusive (issue SqlRSSetup: Document that the properties ProductKey and Edition is mutually exclusive  #1386).

This Pull Request (PR) fixes the following issues

• Fixes Move the CONTRIBUTING.md files together #1227
• Fixes SqlSetup: Does not allow null or empty password for MSA #378
• Fixes SqlSetup: Add documentation around how to use built-in account #1230
• Fixes Integration Tests: Contributing.md should be updated with the different test jobs #1315
• Fixes SqlAGReplica: InnerException: Invalid column name 'required_copies_to_commit' #1033
• Fixes SqlRSSetup: Document that the properties ProductKey and Edition is mutually exclusive  #1386

Task list

• Added an entry to the change log under the Unreleased section of the
  file CHANGELOG.md. Entry should say what was changed and how that
  affects users (if applicable), and reference the issue being resolved
  (if applicable).
• Resource documentation added/updated in README.md.
• Resource parameter descriptions added/updated in README.md, schema.mof
  and comment-based help.
• Comment-based help added/updated.
• Localization strings added/updated in all localization files as appropriate.
• Examples appropriately added/updated.
• Unit tests added/updated. See DSC Community Testing Guidelines.
• Integration tests added/updated (where possible). See DSC Community Testing Guidelines.
• New/changed code adheres to DSC Community Style Guidelines.

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This change is 

[codecov]

Codecov Report

Merging #1576 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1576   +/-   ##
======================================
  Coverage      98%     98%           
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  Files          37      37           
  Lines        6074    6074           
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  Hits         5970    5970           
  Misses        104     104           

[johlju]

Reviewed 7 of 8 files at r1, 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved