Fix issue where copying bullets from the resulting pdf results in text with no whitespace and add `cvsubitems`

[miguelandres]

This solution is based on @chelseanbr's comment from July 28, 2023, https://github.com/posquit0/Awesome-CV/issues/71#issuecomment-1654964285.

Additionally this PR creates a new environment cvsubitems, that is functionally the same as cvitems, with the same workaround to allow reliable copypasting and parsing by ATS systems, but without some adjustments to vertical space that only make sense for cvitems

This fixes #137

Test Plan:

1. run make
2. Open all resulting PDFs and copy text from bullet points into a text editor, review that the copied text has spaces as expected.
3. Add a cvsubitems environment to the first cventry in experience to test that this also works as expected
4. Do the same copypaste test on cv.pdf, guaranteeing that we copy the subitems text.