Allow overwrite of ``output_file`` in ``ccdproc.combiner.combine()``

[tbowers7]

Add an optional keyword argument to ccdproc.combiner.combine() to allow for the overwrite of the optional output_file. The default value of overwrite_output = False is identical to current behavior, and the user would need to specify this keyword argument as True to allow overwriting.

modified:   ccdproc/combiner.py

Please have a look at the following list and replace the "[ ]" with a "[x]" if the answer to this question is yes.

• [ ] For new contributors: Did you add yourself to the "Authors.rst" file?

For documentation changes:

• [ ] For documentation changes: Does your commit message include a "[skip ci]"? Note that it should not if you changed any examples!

For bugfixes:

• [ ] Did you add an entry to the "Changes.rst" file?
• [ ] Did you add a regression test?
• [ ] Does the commit message include a "Fixes #issue_number" (replace "issue_number").
• [ ] Does this PR add, rename, move or remove any existing functions or parameters?

For new functionality:

• [x] Did you add an entry to the "Changes.rst" file?
• [x] Did you include a meaningful docstring with Parameters, Returns and Examples?
• [ ] Does the commit message include a "Fixes #issue_number" (replace "issue_number").
• [ ] Did you include tests for the new functionality?
• [x] Does this PR add, rename, move or remove any existing functions or parameters?

Please note that the last point is not a requirement. It is meant as a check if the pull request potentially breaks backwards-compatibility.

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[codecov[bot]]

Codecov Report

Merging #797 (7686cd8) into main (a5b57ba) will increase coverage by 0.07%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #797      +/-   ##
==========================================
+ Coverage   97.48%   97.55%   +0.07%     
==========================================
  Files           9        9              
  Lines        1390     1390              
==========================================
+ Hits         1355     1356       +1     
+ Misses         35       34       -1     

Impacted Files	Coverage Δ
ccdproc/combiner.py	94.98% <100.00%> (+0.35%)	:arrow_up:

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[mwcraig]

Thanks @tbowers7 -- I'm hoping to do a release later today that includes this so I took the liberty of adding a test to the PR>