implement exportvariable filter

[smoors]

fixes #281

this implements the approach suggested by @boegel in the issue: if the filter is specified in a comment, file bot/export_vars.sh is created and sourced before running the bot/build.sh script

notes:

• as is the case with other filters, spaces or colons cannot be used
• variables have to be specified one by one, which was easier to implement and avoids having to specify another delimiter, which then also cannot be used
• i used filter name exportvariable instead of the suggested build_env to avoid confusion with other uses of build_env in the code.

example usage:

bot: build arch:zen4 export:MYVAR1=myval1 export:MYVAR2=myval2

UPDATE 2024-11-23

• added an allowlist of name-value pairs (allowed_exportvars) to app.cfg for increased security. each name-value pair specified in a PR comment must be listed in the allowlist in order to run a build job.
• moved the export_vars.sh script to the cfg dir

[trz42]

Works as expected. 👍

Thanks a lot @smoors and sorry for the delay in reviewing it.

[trz42]

lgtm

[trz42]

Maybe move this line into the branch that actually sources the script. If the script couldn't be found, it would first echo that it wasn't found and then that it is finished.

[smoors]

fixed in #291