fix(oauth): make OAuth2 Proxy config map mutable

[ebaron]

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Fixes: #984

Description of the change:

• Removes Immutable property from OAuth2 Proxy config map
• Deletes and recreates existing config maps with Immutable: true
• Adds test cases for the config map
• Fixes an issue where passHostHeader and proxyWebSockets were not in the generated JSON

Motivation for the change:

• Allows users to disable cert-manager on an existing Cryostat instance

How to manually test:

1. On Kubernetes, make deploy_bundle BUNDLE_IMG=quay.io/cryostat/cryostat-operator-bundle:3.0.1
2. make create_cryostat_cr
3. Build a bundle image for this PR
4. ./bin/operator-sdk run bundle-upgrade --timeout 5m
5. Check that Immutable property is no longer present in config map
6. Edit CR to disable cert-manager, it should redeploy Cryostat properly

[ebaron]

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