add http client and tlsSecretRef

[Avarei]

Description of your changes

Add http.Client to httpClient.
add mTLS support to CRDs using new tlsSecretRef field which expects a secret containing tls.crt, tls.key, and/or ca.crt

Fixes #21

I have:

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

How has this code been tested

• added test in go
• ran disposablerequest/v1alpha2 with and without tlsSecretRef, with and without ca.crt in the referenced secret. with and without insecureSkipTlsVerify set
• I did NOT test with Request and DisposableRequest/v1alpha1

[Avarei]

still need to redo all tests

[barunavo]

@Avarei : Thanks for this PR, I am waiting for this too. I need it to have possibilities to talk to internal API using Certificate authentication.

[Avarei]

thanks @barunavo for bringing this back to my attention.
I've rebased the changes and added some tests for newClient and the mTLS functionality.
Im still quite new to writing tests so any feedback would be appreciated.

I neeeded to update golangci-lint since the previous version seemed to leak memory on every system I tried to run it.

I also tried this functionality in a cluster using disposablerequests and I could not find any issues so far.

I have not yet used the non-disposable requests and I hope that someone can take a look at them.

[barunavo]

Thanks for the PR @Avarei , may be I will try to take care of the non-disposable request, not sure when I find time.