Use Gotify X-Gotify-Key Header vs params token

[caronc]

Description:

Related issue (if applicable): #556

With respect to documentation here and the related issue above, this request updates Apprise's integration with Gotify to use the HTTP Headers to pass the token along instead of the querystring

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• No lint errors (use flake8)
• 100% test coverage

Testing

Anyone can help test this source code as follows:

# Create a virtual environment to work in
# This way you can just destroy it after when it's all over.
# The below will create a directory called apprise
python3 -m venv apprise

# Change into our new directory
cd apprise

# Activate our virtual environment
source bin/activate

# Install the branch
pip install git+https://github.com/caronc/apprise.git@556-gotify-header-token

# Run your Gotify Tests
apprise gotify://credentials

[codecov-commenter]

Codecov Report

Merging #558 (33cbbc4) into master (4cc5be0) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #558   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          106       106           
  Lines        13696     13695    -1     
  Branches      2544      2544           
=========================================
- Hits         13696     13695    -1     

Impacted Files	Coverage Δ
apprise/plugins/NotifyGotify.py	100.00% <ø> (ø)

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