Interpolation grammar: allow pipe | in unquoted strings

[Jasha10]

This PR adds support for the pipe character | to appear unquoted in OmegaConf's interpolation grammar.
Related to facebookresearch/hydra#1850.

For good measure, I've also added a test for the pipe appearing in quoted strings.

[odelalleau]

Can you also edit (adding both ? and |?):

• omegaconf/omegaconf/grammar_parser.py

  Line 30 in 32e82d3

  _arg = "[a-zA-Z_0-9/\\-\\+.$%*@]+" # string representing a resolver argument

• omegaconf/tests/test_grammar.py

  Line 184 in 32e82d3

  fr"{{a0-null-1-3.14-NaN- {TAB}-true-False-/\+.$%*@\(\)\[\]\{{\}}\:\=\ \{TAB}\,:0}}",

• omegaconf/tests/test_grammar.py

  Line 732 in 32e82d3

  supported_chars = r"abc123_/:-\+.$%*@"

(maybe there should be an UNQUOTED_SPECIAL string like in Hydra that all these tests would re-use?)

[Jasha10]

(maybe there should be an UNQUOTED_SPECIAL string like in Hydra that all these tests would re-use?)

Done in 5f0fad0.

[odelalleau]

Just some minor suggestions

[odelalleau]

Looks good, thanks! Just curious about the CI errors, that seem unrelated => I tried to restart the build but somehow it didn't like it...

[Jasha10]

Looks good, thanks! Just curious about the CI errors, that seem unrelated => I tried to restart the build but somehow it didn't like it...

Yes, I believe the CI errors are unrelated. Jieru and I were trying to fix them in PR #800. I'm not yet sure exactly what's going on -- it seems related to interaction between nox and pip.