Fix issue #22 and simplify project build system

[netops2devops]

The changes made in this commit

• simplify project build system by taking out patches from Makefile into a separate repo esnet/certificates which is a fork of upstream smallstep/certificates

Before this commit - any patches, fixes, workarounds that we had to apply for fixing known limitations in step-ca were applied inside a .build directory which gets created as a part of Makefile

• Our patch for Certbot has a ReadTimeout error if finalization takes >45 seconds with Sectigo's ACME #22 is maintained in a separate repo under branch called patch/v0.30.2

The patch version tag scheme I am following can be seen in go.mod file

[upstream version]-patch.[count]

So if the patches have been applied against upstream v0.30.2 our go.mod should contain

replace github.com/smallstep/certificates => github.com/esnet/certificates v0.30.2-patch.2

Where the trailing patch.2 indicates total count of patches applied so far i.e two. Should we encounter another another bug in upstream v0.30.2 & have to maintain a third patch then we add our fix to github.com/esnet/certificates under branch patch/v0.30.2, test it & create a commit tag with v0.30.2-patch.3.

git tag -a v0.30.2-patch.3 -m "detailed commit message"
git push --tags v0.30.2-patch.3

Update the go.mod in this repo to point to the new tag

replace github.com/smallstep/certificates => github.com/esnet/certificates v0.30.2-patch.3

[lbaker-esnet]

The structure and hygiene work around the upstream dependencies is appreciated, it's much clearer to see what exactly we are patching in.