fix(featuregate): make feature gate independent of controller

[akhilerm]

Signed-off-by: Akhil Mohan akhil.mohan@mayadata.io

Why is this PR required? What issue does it fix?:
The feature gate used to be a part of the daemon controller. This restricted its use to only code paths which had access to the controller pointer. This PR removes the dependency of feature gates on the daemon controller and can be used globally across the code base.

What this PR does?:

• adds a new exporter variable FeatureGates in features package which holds the state of all features.
• remove feature gate from daemon controller

Does this PR require any upgrade changes?:
No

If the changes in this PR are manually verified, list down the scenarios covered::

• tested by providing a set of correct and incorrect feature gates.

Any additional information for your reviewer? :
Mention if this PR is part of any design or a continuation of previous PRs

Checklist:

• Fixes #
• PR Title follows the convention of <type>(<scope>): <subject>
• Has the change log section been updated?
• Commit has unit tests
• Commit has integration tests
• (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
• (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them:

[codecov-commenter]

Codecov Report

Merging #426 into master will decrease coverage by 0.44%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master     #426      +/-   ##
==========================================
- Coverage   44.35%   43.90%   -0.45%     
==========================================
  Files          60       60              
  Lines        2859     2906      +47     
==========================================
+ Hits         1268     1276       +8     
- Misses       1489     1526      +37     
- Partials      102      104       +2     

Impacted Files	Coverage Δ
cmd/ndm_daemonset/controller/controller.go	20.56% <0.00%> (+2.20%)	⬆️
cmd/ndm_daemonset/probe/udevprobe.go	60.56% <0.00%> (-2.82%)	⬇️
cmd/ndm_daemonset/probe/eventhandler.go	10.82% <100.00%> (-1.55%)	⬇️
pkg/features/features.go	100.00% <100.00%> (ø)

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[kmova]

n_: DefaultFeatureGates => FeatureGates or a generic name as it contains both default and those enabled via ENV etc,. right?

[akhilerm]

FeatureGates was not used because there is already a FeatureGate type in the same package.

Do you have suggestion for any other generic names?

[akhilerm]

FeatureGate will renamed to featureFlag, and DefaultFeatureGates to FeatureGates