Suppress unnecessary changes to connection limits by checking existing value for PostgreSQL

[ajcaldera1]

Description of your changes

This change checks the state of the connection limit for a Postgres role prior to mutating it. The previous behavior would blindly fire the ALTER ROLE CONNECTION LIMIT -1 even if there was no change. Added test to verify connection limit settings were being properly mutated. Corrected a couple of instances of kubectl being referenced in the tests that caused them to fail, replaced with shell variable ${KUBECTL}.

Fixes #194

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.

How has this code been tested

Added test to e2e suite to verify the connection limit and review Postgres logs to ensure that no statement had been fired when it was unnecessary.

[chlunde]

@ajcaldera1 Awesome, looking forward to this! Could you squash or rebase it, and make sure you've added DCO for your commit? At the moment the button to run CI is not enabled, I suspect it is related to the fact that this contains 24 commits with many merged 😄

[chlunde]

Could you do this in a separate PR?

Would rather have many smaller PRs which focus on one feature, thanks!

[chlunde]

Why the three casts to int64? Could we simply drop then?

[chlunde]

The default here is unlimited, represented as -1?

Could we do this instead, or do you see any issues with this?

Suggested change

	newCl := cr.Spec.ForProvider.ConnectionLimit
	currCl := cr.Status.AtProvider.ConnectionLimit
	if (newCl != nil && currCl != nil) && (int64(*currCl) != int64(*newCl)) {
	newCl := ptr.Deref(cr.Spec.ForProvider.ConnectionLimit, -1)
	currCl := ptr.Deref(cr.Status.AtProvider.ConnectionLimit, -1)
	if currCl != newCl {

[chlunde]

Don't you also need this ptr.Deref-ing in

func upToDate(observed *v1alpha1.RoleParameters, desired *v1alpha1.RoleParameters) bool {
	if observed.ConnectionLimit != desired.ConnectionLimit {
		return false
	}

to

func upToDate(observed *v1alpha1.RoleParameters, desired *v1alpha1.RoleParameters) bool {
	if ptr.Deref(observed.ConnectionLimit, -1) != ptr.Deref(desired.ConnectionLimit, -1) {
		return false
	}

Could you add some tests for Observe or upToDate covering this case?