Added delay= switch to aprs:// plugin

[caronc]

Description:

Related issue (if applicable): #1105

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 as follows:
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@1105-aprs-delay-switch

# Test out the changes with the following command:
apprise -t "Test Title" -b "Test Message" \
  aprs://credentials?delay=2.0

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.27%. Comparing base (cced5ed) to head (f0322e4).
Report is 3 commits behind head on master.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1107   +/-   ##
=======================================
  Coverage   99.27%   99.27%           
=======================================
  Files         139      139           
  Lines       18029    18045   +16     
  Branches     3680     3685    +5     
=======================================
+ Hits        17899    17915   +16     
  Misses        121      121           
  Partials        9        9           

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