Allow numbers and symbols on yaml context

[nkarab]

Problem and/or solution

So far, we've been able to include context in YAML files (YAML_GENERIC, YML i18n) tx doc by utilizing custom YAML tags .
For instance:

string: !context translation 

However, our Yaml parser for the context only allows alphabetic characters, zeros, and underscores. For instance:

a_string_without_context: !context1 translation  # context -> None
a_string_with_context: !context_smth translations  # context -> !context_smth

We have now extended support to include numbers and a limited set of special symbols namely (- _ : .).

Additionally, the context is stored in our database with the exclamation mark, and we aim to remove it.

backwards compatibility
slack conversation about it: https://transifex.slack.com/archives/C01BHGRAGH1/p1693309705338759

How to test

Upload a YML i18n and a YAML_GENERIC resource file that includes custom tags featuring numbers or special symbols.

en:
  context_string: !he:fd94_fd-la. "context string"
  verbim_context_string: !<!context545qa> "verbim context string"
  context_on_nested_map:
    first: !first_context:54KJFLA95KJ4 "context in nested map"
    second: !second_context:FDKJ40DK "context in nested map"

We expect these contextes:

string key	context
context_string	he:fd94_fd-la.
verbim_context_string	context545qa
context_on_nested_map.first	first_context:54KJFLA95KJ4
context_on_nested_map.second	second_context:FDKJ40DK

We expect a downloaded file for the source language like this:

en:
  context_string: !he:fd94_fd-la. "context string"
  verbim_context_string: !context545qa "verbim context string"
  context_on_nested_map:
    first: !first_context:54KJFLA95KJ4 "context in nested map"
    second: !second_context:FDKJ40DK "context in nested map"

We expect for the translation language a file like this:

el:
  context_string: !he:fd94_fd-la. ""
  verbim_context_string: !contex545qa ""
  context_on_nested_map:
    first: !first_context:54KJFLA95KJ4 ""
    second: !second_context:FDKJ40DK ""
    

Staging: https://yamlcntxt.stg.transifex.net/

Reviewer checklist

Code:

• Change is covered by unit-tests
• Code is well documented, well styled and is following best practices
• Performance issues have been taken under consideration
• Errors and other edge-cases are handled properly

PR:

• Problem and/or solution are well-explained
• Commits have been squashed so that each one has a clear purpose
• Commits have a proper commit message according to TEM

[fathineos]

Let's add a test case with !! as well

[fathineos]

Let's add a test case with !! as well

ignore my comment, I see that we already have such tests in place

[kbairak]

Looks great! The comment is optional.

[kbairak]

Why not \w instead of a-zA-Z0-9?

[kbairak]

The linter is not going to like this.