feat: Allow users to disable extauth sidecar on a per proxy basis

[davidjumani]

Description

When multiple gateway proxies are defined as well as extauth enabled, a user might want to enable the sidecar for a subset of gateway proxies (since some of them do not require extauth) to reduce resource usage and unnecessary network calls to an unused sidecar.
This feature adds the new helm value gatewayproxy.proxyName.disableExtauthSidecar to disable the extauth sidecar on it
It also adds additional helper methods to merge resources while omitting keys in those resources which should not be overwritten if empty

Helm changes

• Added a new gatewayproxy.proxyName.disableExtauthSidecar value

Code changes

N/A

CI changes

N/A

Docs changes

N/A

Context

#8430

Interesting decisions

Had initially thought of the idea to omit fields in an overwrite based on keys as in ddc6774 but decided against it as future changes would require modifying those keys if the same field is modified in different locations. Eg: if one part of the code did not want the field modified it would add the key to the list of omitKeys but another part of the code when changing the field would need to remove it from the list

Testing steps

Unit tests in enterprise to validate the behaviour of the new helm fields and helpers

Notes for reviewers

N/A

Please proofread comments on ...

N/A

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

[solo-changelog-bot]

Issues linked to changelog:
#8430

[github-actions]

Visit the preview URL for this PR (updated for commit e190aea):

https://gloo-edge--pr8898-disable-extauth-side-8ks7trcg.web.app

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[sheidkamp]

One nit, but LGTM