feat: Add ability to specify MTU when creating Network

[tasdikrahman]

What type of PR is this?

/kind feature

What this PR does / why we need it:

User can set GCPCluster.Spec.Network.Mtu for setting the MTU for the network being created. If nothing is passed the MTU will default to 1440 which is the default set here https://cloud.google.com/vpc/docs/mtu

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #1246

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

feat: Add ability to add GCPCluster.Spec.Network.Mtu 

[k8s-ci-robot]

Hi @tasdikrahman. Thanks for your PR.

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[cpanato]

/ok-to-test

[tasdikrahman]

Thanks for the review @cpanato , let me know if you would like me to add any more changes on this PR before approval. Thank you.

[cpanato]

thanks

/approve

/assign @damdo

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, tasdikrahman

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[damdo]

I think we should add openAPI validation for this field only allowing the two values you are mentioning.
Also where are those values coming from? We might want to leave a message mentioning that.

[damdo]

Also we could add a validation step in the validation code (e.g. webooks).
And a couple of unit test checking that is validated correctly.

[tasdikrahman]

I think we should add openAPI validation for this field only allowing the two values you are mentioning.
Also where are those values coming from? We might want to leave a message mentioning that.

Hello there, I fixed the validation code to have the minimum and maximum values present. The values of minimum of 1300 and maximum of 8896 are taken from https://pkg.go.dev/google.golang.org/api/compute/v1#Network

Also we could add a validation step in the validation code (e.g. webooks).
And a couple of unit test checking that is validated correctly.

Will add some unit tests exercising this.

[damdo]

/hold
For changes to be added

[damdo]

Thank you for implementing the requested changes @tasdikrahman
/lgtm
/unhold