New rule to flag special characters in identifiers

[jpers36]

Fixes #1746

Brief summary of the change made

A new linting rule: flag special characters in identifiers.

If an identifier includes a character other than alphanumeric or underscore, this rule will flag it.
This rule includes configuration settings to control which types of identifiers fall under the rule.
This rule also includes a configuration setting to allow or disallow spaces as part of an identifier.

+L057 python script
+L057 test YAML
+L057 configuration defaults
+allow_space_in_identifier description in config_info.py

[codecov]

Codecov Report

Merging #1958 (465f286) into main (67023b8) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main     #1958   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          147       148    +1     
  Lines        10284     10300   +16     
=========================================
+ Hits         10284     10300   +16     

Impacted Files	Coverage Δ
src/sqlfluff/core/rules/config_info.py	100.00% <ø> (ø)
src/sqlfluff/rules/L057.py	100.00% <100.00%> (ø)

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[jpy-git]

few quick tweaks whilst i look through the rule logic

[jpy-git]

@jpers36 a couple suggestions formatting wise, plus note on typing, and extra unit tests suggestions.
For the most part its looking great! 💪

(always find it a bit mad that sql allows these non alnum characters)

[jpy-git]

Looks good! 🥇

[jpy-git]

@barrywhart I don't have write access so can't approve.

I've looked over the code and all feedback has been addressed so can you take a quick look over and if there's nothing else to add then approve and merge 😄