feat: double_quotes

[simojoe]

This pull request adds a new rule to wdl.

• Rule Name: double_quotes
• Rule Kind: Lint warning
• Rule Code: v1::W012
• Packages: wdl-grammar

Warns about strings defined with single-quotes. This ignores anything located inside the command section. Tests are not exhaustive, there are quite a lot of things that are using strings. Should they still be added?

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• [X] You have added a few sentences describing the PR here.
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Rule specific checks:

• [X] You have added the rule as an entry within the the package-specific rule tables (wdl-ast/src/v1.rs for AST-based rules and wdl-grammar/src/v1.rs for parse tree-based rules).
• [X] You have added the rule as an entry within the the global rule table at RULES.md.
• [X] You have added the rule to the appropriate fn rules().
  • Validation rules added to wdl-ast should be added to fn rules() within wdl-ast/src/v1/validation.rs.
  • Lint rules added to wdl-ast should be added to fn rules() within wdl-ast/src/v1/lint.rs.
  • Validation rules added to wdl-grammar should be added to fn rules() within wdl-grammar/src/v1/validation.rs.
  • Lint rules added to wdl-grammar should be added to fn rules() within wdl-grammar/src/v1/lint.rs.
• [ ] You have added a test that covers every possible setting for the rule within the file where the rule is implemented.
• [X] You have run wdl-gauntlet --save-config to ensure that all of the rules added/removed are now reflected in the baseline configuration file (Gauntlet.toml).