ngsild-tenant header support

Proposed changes

This PR makes Quantum Leap use the NGSI-LD tenant header if present in a request. If there's no NGSI-LD tenant header, we fall back to the FIWARE service header we all know and love. Notice if both headers are present, the NGSI-LD tenant takes precedence.

The code in this PR was originally contributed by @rohit-vrrr in #695. We're only porting it over to a new branch because we needed to rebase @rohit-vrrr's branch to be able to merge.

Types of changes

What types of changes does your code introduce to the project?

[x] 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)
[ ] Maintenance (update of libraries or other dependences)

Checklist

[x] I have read the CONTRIBUTING doc
[x] I have signed the CLA
[x] I have added tests that prove my fix is effective or that my feature works
[x] I have run all the existing tests locally (not just those related to my feature) and there are no errors
[x] After the last push to the PR branch, I have run the lint script locally and there are no changes to the code base
[x] I have updated the RELEASE NOTES
[x] I have added necessary documentation (if appropriate)
[x] Any dependent changes have been merged and published in downstream modules

Further comments

N/A

"Martel Open Source Software Individual Contributor License Agreement"

"Contributing to QuantumLeap"

"QuantumLeap Release Notes"

orchestracities / ngsi-timeseries-api