Add multiversional testing scripts

[mkgrgis]

This scripts allows automatically get multiversional PostgreSQL source codes from official PGDG repository. With some untested limitations this is applicable also to other pgspider FDWs with ./test.sh script in root source code directory.

No C-language review, please let review by compilation environment infrastructure engineers.

[t-kataym]

@mkgrgis , Thank you for the PR.
Please let me share our opinion.
The source code of testing target is downloaded from GitHub. It means that your scripts can be run outside of sqlite_fdw.
FDWs in our projects support multi versions of PostgreSQL as same as sqlite_fdw.
We think your scripts is useful for the other our FDWs.
So we would like to create a new repository in PGSpider project and put your scripts in if you agree.

[mkgrgis]

Yes, I am agree, @t-kataym ! Please only describe me as author of this first edition of the scripts.

[mkgrgis]

pgspider/testing_scripts ?

[t-kataym]

@mkgrgis , We would like to proceed with the following steps if you agree. It can indicate that you are the first author of the scripts.

1. You publish these scripts as OSS on GItHub repository on your account. We expect the license is PostgreSQL License.
2. We fork your repository into PGSpider project.
3. You create PR on our repository if you need.

[mkgrgis]

Thanks, @t-kataym ! All is done https://github.com/mkgrgis/fdw_testing_scripts , please fork and use. You can close this PR after this as implemented in other way.

[t-kataym]

@mkgrgis , Thank you for your understanding.
Could you remove the our name "Toshiba Corporation" from Copyright because only you created scripts and we didn't do anything for the scripts now?
When we modify the source code or comment the PR, we would like to append our name to Copyright.

[mkgrgis]

Could you remove the our name "Toshiba Corporation" from Copyright because only you created scripts and we didn't do anything for the scripts now?

Yes, fixed. Please verify.

[t-kataym]

@mkgrgis , Thank you for fixing and your contribution.
I forked your repository just now.
https://github.com/pgspider/fdw_testing_scripts

So I would like to close the PR.

[mkgrgis]

Thanks for accepting my contribution. @t-kataym !