[pkg/ottl] Fix escape sequences in strings

[quentinmit]

Description:

Fix ottl parsing to properly handle escape sequences.
@TylerHelmuth

Link to tracking Issue:
#23238

Testing:
Added a new unit test with the example from the linked issue

Documentation:
None (pure bugfix)

[TylerHelmuth]

Thanks for finding this solution - I remember spending a while on that regex and was unable to come up with a suitable replacement.

Please add some new scenarios in e2e that put strings to the test. Some scenarios I think would be useful:

• Using a string that is a single backslash
• Using a string that is 2 backslashes
• Using a string that is 3 backslashes
• Using a string that is 4 backslashes
• A test for the a("\\", "b") scenario.

plus any edge cases you can think of.

[quentinmit]

@TylerHelmuth Alright, I added several tests to e2e_test.go for this.

[TylerHelmuth]

I am happy that the new and existing test cases prove this regex works. @evan-bradley please review

[TylerHelmuth]

@quentinmit please add a bug_fix changelog entry

[evan-bradley]

Thank you @quentinmit!

Can you update ottlfuncs/README.md to remove all references to #23238?

[quentinmit]

@evan-bradley @TylerHelmuth I added a changelog entry and updated the README. Thanks!