[#651] regex compatability for headers matching

[geetptl]

Attempt at #651.

• Changes in header_matcher function.
• Instead of using simple list equality, it now checks for either regex or simple string check.
• Added tests test_request_matches_headers_regex, test_request_matches_headers_regex_strict_match

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (ad22f54) 100.00% compared to head (a2e2da1) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #663 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 9 9 Lines 2880 2968 +88 ========================================= + Hits 2880 2968 +88 ``` | [Files Changed](https://app.codecov.io/gh/getsentry/responses/pull/663?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | Coverage Δ | | |---|---|---| | [responses/matchers.py](https://app.codecov.io/gh/getsentry/responses/pull/663?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry#diff-cmVzcG9uc2VzL21hdGNoZXJzLnB5) | `100.00% <100.00%> (ø)` | | | [responses/tests/test\_matchers.py](https://app.codecov.io/gh/getsentry/responses/pull/663?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry#diff-cmVzcG9uc2VzL3Rlc3RzL3Rlc3RfbWF0Y2hlcnMucHk=) | `100.00% <100.00%> (ø)` | |

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[markstory]

Thank you 🎉