Basic devcontainer config

[krissetto]

- What I did

• Added an initial devcontainer configuration to facilitate development on the codebase;
• Updated README/CONTRIBUTING docs with some extra info on setting up a local development environment and using a devcontainer;
• Added dependabot config to check for updates weekly

- How to verify it

• Pull and test the config using an ide like vscode
• Proof-read doc changes :)

- Description for the changelog

Added initial devcontainer configuration

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Merging #4845 (1d92d8c) into master (2936816) will increase coverage by 1.69%. Report is 691 commits behind head on master. The diff coverage is 61.90%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4845      +/-   ##
==========================================
+ Coverage   59.58%   61.28%   +1.69%     
==========================================
  Files         288      287       -1     
  Lines       24821    20029    -4792     
==========================================
- Hits        14790    12275    -2515     
+ Misses       9145     6864    -2281     
- Partials      886      890       +4