use random grpc port

[nthnieljson]

KubeArmor/config/config.go : define a constant for the pid file path
KubeArmor/feeder/feeder.go : use a random grpc port number and save it to a file

previously we can't use random grpc port

now we can use random grpc port number by specifying "0" as the port number, by using port number 0, we will listen on random port and then we save the random port number to a pid file located in /opt/kubearmor

Signed-off-by: nthnieljson nthnieljson@gmail.com

[nthnieljson]

this is addressing the issue on #623 to use random grpc port number

[seswarrajan]

LGTM. @nyrahul need to approve.

[codecov-commenter]

Codecov Report

Merging #672 (38028e1) into main (925a26a) will decrease coverage by 7.46%.
The diff coverage is 9.67%.

@@            Coverage Diff             @@
##             main     #672      +/-   ##
==========================================
- Coverage   43.35%   35.89%   -7.47%     
==========================================
  Files          23       25       +2     
  Lines        8530     9033     +503     
==========================================
- Hits         3698     3242     -456     
- Misses       4378     5336     +958     
- Partials      454      455       +1     

Impacted Files	Coverage Δ
KubeArmor/config/config.go	85.85% <ø> (+1.95%)	⬆️
KubeArmor/monitor/systemMonitor.go	48.06% <0.00%> (-1.28%)	⬇️
KubeArmor/feeder/feeder.go	53.10% <16.66%> (-0.94%)	⬇️
KubeArmor/monitor/syscallParser.go	54.54% <0.00%> (-23.71%)	⬇️
KubeArmor/feeder/policyMatcher.go	37.56% <0.00%> (-3.09%)	⬇️
KubeArmor/core/kubeUpdate.go	43.68% <0.00%> (-1.10%)	⬇️
KubeArmor/enforcer/appArmorEnforcer.go	48.29% <0.00%> (-0.60%)	⬇️
KubeArmor/enforcer/SELinuxEnforcer.go	0.00% <0.00%> (ø)
KubeArmor/enforcer/appArmorHostProfile.go	0.00% <0.00%> (ø)
... and 9 more

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[nyrahul]

Thanks @nthnieljson for handling this. LGTM.

So as i understand the logic is:
If GRPC config is set to 0, then we listen on port 0 which means we will get a dynamically allocated port, whose value will be written in the pid file.
There is another PR in kubearmor-client which will check for this pid file and use the port number.

@nam-jaehyun , WDYT? I like this solution.

[nam-jaehyun]

@nthnieljson can you make all the changes in a single commit in order to merge this PR?

[nam-jaehyun]

after squashing the commits, let's merge the PR.