add AccessKey schema and update flyway location

[nobodyiam]

What's the purpose of this PR

1. Add AccessKey schema for Implement #2099，添加apollo-client的身份认证功能及accesskey管理功能 #2828
2. Update flyway migration location

Which issue(s) this PR fixes:

#2828

Brief changelog

1. Add AccessKey schema
2. Update flyway location from scripts/db/migration to scripts/flyway
3. Add back scripts/sql/apolloconfigdb.sql and scripts/sql/apolloportaldb.sql so that people who don't use flyway can still have an easy way to import schemas

Follow this checklist to help us incorporate your contribution quickly and easily:

• Read the Contributing Guide before making this pull request.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit tests to verify the code.
• Run mvn clean test to make sure this pull request doesn't break anything.

[codecov-io]

Codecov Report

Merging #2883 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2883   +/-   ##
=========================================
  Coverage     50.65%   50.65%           
  Complexity     2148     2148           
=========================================
  Files           425      425           
  Lines         13055    13055           
  Branches       1337     1337           
=========================================
  Hits           6613     6613           
  Misses         5974     5974           
  Partials        468      468

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[coveralls]

Coverage remained the same at 54.24% when pulling f3ef478 on nobodyiam:access-key-schema into 32aac0b on ctripcorp:master.