Update bitbucket related documentation with known issues and process workarounds

Need some fixes to the bitbucket related documentation for Che/CRW https://www.eclipse.org/che/docs/che-7/administration-guide/authenticating-users-3rd-party-services/#configuring_bitbucket_authentication_che

• fix BitBucket token configuration instructions
• add link to the article with instrucions about configuring CRW to use git server with self-signed certificate https://www.eclipse.org/che/docs/che-7/installation-guide/deploying-che-with-support-for-git-repositories-with-self-signed-certificates/

Follows up from CRW-1372