Includes support to get container logs from the pod, Kubernetes API auto configuration and lots of bug fixes

The full changelog:

• containerLog step to get the logs of a container running in the agent pod JENKINS-46085 #195
• Autoconfigure cloud if kubernetes url is not set #208
• Change containerCap and instanceCap 0 to mean do not use JENKINS-45845 #199
• Add environment variables to container from a secret JENKINS-39867 #162
• Deprecate containerEnvVar for envVar and added secretEnvVar
• Enable setting slaveConnectTimeout in podTemplate defined in pipeline #213
• Read Jenkins URL from cloud configuration or KUBERNETES_JENKINS_URL env var #216
• Make withEnv work inside a container JENKINS-46278 #204
• Close resource leak, fix broken pipe error. Make number of concurrent requests to Kubernetes configurable JENKINS-40825 #182
• Delete pods in the cloud namespace when pod namespace is not defined JENKINS-45910 #192
• Use Util.replaceMacro instead of our custom replacement logic. Behavior change: when a var is not defined it is not replaced, ie. ${key1} or ${key2} or ${key3} -> value1 or value2 or ${key3} #198
• Allow to create non-configurable instances programmatically #191
• Do not cache kubernetes connection to reflect config changes and credential expiration JENKINS-39867 #189
• Inherit podAnnotations when inheriting pod templates #209
• Remove unneeded plugin dependencies, make pipeline-model-extensions optional #214