Fix subscription config and doctests

[woop]

What this PR does / why we need it:
#525 has caused some inconsistencies with e2e tests. I believe it was merged without proper e2e tests running.

This PR attempts fix to inconsistencies.

• Subscriptions configuration isn't loading because the configuration class isn't static.
• JavaDocs are broken (bad links)

Does this PR introduce a user-facing change?:

None

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: woop

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [woop]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[woop]

/test test-end-to-end-batch

[woop]

/test test-end-to-end

[woop]

/retest

[woop]

/test test-end-to-end-batch

[woop]

/test test-end-to-end

[feast-ci-bot]

@woop: The following tests failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
test-end-to-end	d1fce36	link	/test test-end-to-end
test-end-to-end-batch	d1fce36	link	/test test-end-to-end-batch

Full PR test history

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.