Externailize dependency on operator-sdk so it's not hardcoded in 4 scripts

[nickboldt]

Is your enhancement related to a problem? Please describe.

Mykhailo installed operator-sdk 0.17.2, because in https://github.com/eclipse/che-operator/blob/master/olm/update-nightly-bundle.sh#L34 it says that 0.17.x is required and 0.17.2 is the latest.

Then the build failed...

Error:  operator-sdk v0.17.1 is required. Aborting.
Error: Process completed with exit code 1.

-- https://github.com/eclipse/che-operator/runs/1426532323?check_suite_focus=true

... even though it includes 0.17.2:

https://github.com/eclipse/che-operator/blob/master/.github/workflows/release.yml#L57

... because OTHER scripts explicitly hardcodedly depend on 0.17.1.

** [1] ./go.mod ** 
15:	k8s.io/apimachinery v0.17.1

** [2] ./make-release.sh ** 
48:  [[ $(operator-sdk version) =~ .*v0.17.1.* ]] || { echo "[ERROR] operator-sdk v0.17.1 is required. Aborting."; exit 1; }

** [3] ./olm/docker-run.sh ** 
20:OPERATOR_SDK_VERSION=v0.17.1

** [4] ./olm/update-crd-files.sh ** 
34:  [[ $operatorVersion =~ .*v0.17.1.* ]] || { echo "operator-sdk v0.17.1 is required"; exit 1; }

** [5] ./vendor/modules.txt ** 
199:# k8s.io/apimachinery v0.17.1 => k8s.io/apimachinery v0.0.0-20191004115801-a2eda9f80ab8

and

** [6] ./olm/update-nightly-bundle.sh ** 
34:    echo "This script requires Operator SDK v0.17.x. Please install the correct version to continue"

Describe the solution you'd like

Move the variable OPERATOR_SDK_VERSION=v0.17.1 into a text file called VERSION or REQUIREMENTS or something.
Load that file when running the shell scrupt, and validate installed operator-sdk version using that version so it's consistent across all scripts.

Describe alternatives you've considered

Keep it hardcoded in 3 scripts and 2 go config files, and occasionally break the build if not all files are updated consistently.

Additional context