Add support for access-log-path and error-log-path

[maxlaverse]

By default, the access logs of the Nginx Ingress go to /var/log/nginx/access.log which is a synlink to /dev/stdout. We are using a syslog server to store all our access logs which leaves us with two options:

• parsing the access logs out of the container stdout
• modifying the template to specify a different destination (our syslog server)

For performance reason and simplicity we choose to directly send our logs from Nginx to a syslog service. This is working fine by modifying the template.

However, since it might interest other people to have the log destination customizable, a cleaner solution would be to make it configurable in the ConfigMap and that's what this PR is about.

This pull-requests adds support for a access-log-path field in the Nginx ConfigMap to set a different path than the default one (/var/log/nginx/access.log). The value is put as is in the Nginx template, therefore also allowing to configure a syslog server as log destination.

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[k8s-reviewable]

This change is 

[coveralls]

Coverage increased (+0.007%) to 44.321% when pulling 9049b93 on maxlaverse:custom_access_log_path into e7d2ff6 on kubernetes:master.

[coveralls]

Coverage increased (+0.007%) to 44.321% when pulling 9049b93 on maxlaverse:custom_access_log_path into e7d2ff6 on kubernetes:master.

[coveralls]

Coverage increased (+0.007%) to 44.321% when pulling 39de6bd on maxlaverse:custom_access_log_path into e7d2ff6 on kubernetes:master.

[aledbf]

Why not also add a variable for error_log?

[maxlaverse]

I just made it configurable in the PR since I hadn't any reason not to add it

[aledbf]

@maxlaverse please squash the commits

[coveralls]

Coverage increased (+0.01%) to 44.328% when pulling dd00b6d on maxlaverse:custom_access_log_path into e7d2ff6 on kubernetes:master.

[coveralls]

Coverage decreased (-0.01%) to 44.303% when pulling dd00b6d on maxlaverse:custom_access_log_path into e7d2ff6 on kubernetes:master.

[coveralls]

Coverage increased (+0.03%) to 44.341% when pulling dd00b6d on maxlaverse:custom_access_log_path into e7d2ff6 on kubernetes:master.

[coveralls]

Coverage increased (+0.01%) to 44.328% when pulling dd00b6d on maxlaverse:custom_access_log_path into e7d2ff6 on kubernetes:master.

[aledbf]

/lgtm

[aledbf]

@maxlaverse thanks!