Support Custom Gitlab Instance

[4xpl0r3r]

Summary:
This PR makes the code supporting custom Gitlab instance, merged 3 GITLAB_ENTERPRISE_* configs into 1 GITLAB_HOST.

Description for the changelog:

1. merge 3 GITLAB_ENTERPRISE_* configs into 1 GITLAB_HOST.
2. add the host parameter for Gitlab clientOptions to support custom Gitlab instances.

Other info:
I have tested the code, it works well with my community edition gitlab instance. It seems like the config names GITLAB_ENTERPRISE_*, which are similar to the Github's, are not proper names for Gitlab because there could be both community edition and enterprise edition of custom Gitlab. Therefore, I merged these 3 configs into 1 GITLAB_HOST.

Have a nice day.

[4xpl0r3r]

This is my example of env file

GITLAB_CLIENT_ID=0000000000000000000000000000000
GITLAB_CLIENT_SECRET=gloas-0000000000000000000000000000000
GITLAB_SCOPE=read_user read_repository write_repository profile read_api api
GITLAB_REDIRECT_URI=http://threat-dragon-instance/api/oauth/return
GITLAB_HOST=http://gitlab-instance

[4xpl0r3r]

#947 Ref

[jgadsden]

apologies for being slow to review this @4xpl0r3r , the pull request is much appreciated and I hope to look at it this weekend

[4xpl0r3r]

apologies for being slow to review this @4xpl0r3r , the pull request is much appreciated and I hope to look at it this weekend

Don’t mind, no problem.

[jgadsden]

@4xpl0r3r I thought we needed the env variables 'ENTERPRISE_HOSTNAME', 'ENTERPRISE_PROTOCOL' and 'ENTERPRISE_PORT' for running gitlab enterprise?
This is being discussed in #947 if I understand correctly @steve-winter and @fdellwing ?

[4xpl0r3r]

@4xpl0r3r I thought we needed the env variables 'ENTERPRISE_HOSTNAME', 'ENTERPRISE_PROTOCOL' and 'ENTERPRISE_PORT' for running gitlab enterprise? This is being discussed in #947 if I understand correctly @steve-winter and @fdellwing ?

I believe we should merge GITLAB_ENTERPRISE_* into GITLAB_HOST because of the following reasons:

1. There could be both community and enterprise edition of self-hosted gitlab instances. ENTERPRISE might be misleading.
2. The underlaying gitbeaker is using clientOptions.auth['host'] to indicate the Gitlab instance to connect, pass the direct host option could be more clear than 3 options.

Just my personal understanding, it is ok to keep the original names in case there is any concern I missed.

[fdellwing]

I totally missed this PR, so sorry for the late response and thanks for the ping.

I tested the PR and it seems to work fine.

I'm in support of merging the 3 keys into GITLAB_HOST. There was no need to use 3 keys in the first place, as all they there used for was to construct the host itself.

[jgadsden]

OK, thanks @fdellwing and @4xpl0r3r I will go ahead and merge
Could either of you provide a step by step on how to access GitLab? We have an open issue in the documentation: Add step by step for gitlab access #81