Issue 328: Add support of customized volumeMounts for zookeeper container

[CraneShiEMC]

Change log description

Added a new field volumeMounts in ZookeeperClusterSpec so that users can set customized volumeMounts for zookeeper container to mount customized volumes user specified.

Purpose of the change

Fixes #328

What the code does

Added a new field volumeMounts in ZookeeperClusterSpec and the customized volumeMounts specified can be added to the zookeeper container.

How to verify it

Verified that able to configure customized volumeMounts for zk container and successfully mounted the customized volumes to the zk container.

[realAaronWu]

Please add UT coverage for the Spec.VolumeMounts.

[codecov-commenter]

Codecov Report

Merging #327 (a8c3ea3) into master (a99c93b) will decrease coverage by 1.54%.
The diff coverage is 35.71%.

@@            Coverage Diff             @@
##           master     #327      +/-   ##
==========================================
- Coverage   84.67%   83.13%   -1.55%     
==========================================
  Files          11       11              
  Lines        1312     1352      +40     
==========================================
+ Hits         1111     1124      +13     
- Misses        133      157      +24     
- Partials       68       71       +3     

Impacted Files	Coverage Δ
...g/apis/zookeeper/v1beta1/zookeepercluster_types.go	98.68% <ø> (ø)
...kg/apis/zookeeper/v1beta1/zz_generated.deepcopy.go	88.97% <32.50%> (-11.03%)	⬇️
pkg/zk/generators.go	99.27% <100.00%> (ø)

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[CraneShiEMC]

Please add UT coverage for the Spec.VolumeMounts.

Added now

[anishakj]

LGTM