Adding parameter to configure max HTTP header size

Proposed changes

During authorization, clients might send requests with very large JWTs, e.g., in case that these contain a full certificate chain in the x5c header. Per default, the node express webserver only accepts headers up to 8KB. This change allows to set a different (higher) value via an ENV. If not specified, it uses the default value of 8192 bytes.

Types of changes

What types of changes does your code introduce to the project: Put an x in the boxes that apply

[ ] Bugfix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

[x] I have read the CONTRIBUTING doc
[x] I have signed the CLA
[ ] I have added tests that prove my fix is effective or that my feature works
[x] I have added necessary documentation (if appropriate)
[ ] Any dependent changes have been merged and published in downstream modules

Further comments

Since this needs to be provided as parameter to the node start command, this is only configurable via an ENV.

ging / fiware-idm