Which chart:
nginx:9.2.0

Describe the bug
The chart always mounts /opt/bitnami/nginx/conf/server_blocks path. This mean that any preexisting *.conf file are ignored.

To Reproduce
Steps to reproduce the behavior:

1. create a custom bitnami nginx docker image
2. customize the image by placing additional *.conf files in /opt/bitnami/nginx/conf/server_blocks (or in any subdirectory)
3. deploy the chart using the custom docker image
4. the pod may fail (e.g. the missing server_block declared a variable using map; the variable is not found during initialization) or behave unexpectedly (e.g. the missing server block exposed something else on a different port; nginx does not reply to the port)

Expected behavior
The chart should not mount the path /opt/bitnami/nginx/conf/server_blocks by default. It should do that only if it requires to write additional files to it (i.e. if one of those values are declared: .Values.serverBlock, .Values.ldapDaemon.enabled. .Values.existingServerBlockConfigmap).

Another solution would be to allow the user to disable the mount with an additional value.

NOTE: this bug can currently be circumvented by declaring the same server block using the .Values.serverBlock value.

Version of Helm and Kubernetes:

• Output of helm version:

version.BuildInfo{Version:"v3.5.3", GitCommit:"041ce5a2c17a58be0fcd5f5e16fb3e7e95fea622", GitTreeState:"dirty", GoVersion:"go1.15.8"}

• Output of kubectl version:

Client Version: version.Info{Major:"1", Minor:"20", GitVersion:"v1.20.5", GitCommit:"6b1d87acf3c8253c123756b9e61dac642678305f", GitTreeState:"clean", BuildDate:"2021-03-18T01:10:43Z", GoVersion:"go1.15.8", Compiler:"gc", Platform:"windows/amd64"}
Server Version: version.Info{Major:"1", Minor:"19", GitVersion:"v1.19.7", GitCommit:"1dd5338295409edcfff11505e7bb246f0d325d15", GitTreeState:"clean", BuildDate:"2021-01-13T13:15:20Z", GoVersion:"go1.15.5", Compiler:"gc", Platform:"linux/amd64"}