Update OSPR bot for the Atlassian migration

[nedbat]

• Remove most of the hard-coding of openedx.atlassian.net
• Change the JIRA server to 2u-internal.atlassian.net
• Make JIRA optional (JIRA_SERVER="" turns off Jira activity)

For using GitHub projects:

• Add pull requests to a GitHub project
• Add blended pull requests to a separate GitHub project

[hurtstotouchfire]

Split off:

• Update bot after OEP 55 is further along
  & close the remainder