Added new button styles to Style Guide, Patterns pg [ref #6940]

[mheppler]

What this PR does / why we need it:

Added new button styles with code example to Style Guide, Patterns pg.

Which issue(s) this PR closes:

Closes #6940 Style Guide - Review and update UI references for new btn's on dataset and file pgs

Special notes for your reviewer:

N/A

Suggestions on how to test this:

Build guides in Sphinx. See screenshot in issue.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

N/A

Is there a release notes update needed for this change?:

N/A

Additional documentation:

N/A

[coveralls]

Coverage remained the same at 19.557% when pulling d15feb7 on 6940-style-guide-new-buttons into b97185a on develop.

[TaniaSchlatter]

I'd like the guides to include an example of the "Access" button on a file page, and describe:

• the visual hierarchy of more important buttons being stronger color
• grouping Download and Explore options

I'd like the description of the icon only buttons to include that there can be up to 3 of these buttons for a file, and that if there are more than 3, one of the three should be a "kebab" icon with a dropdown.

[mheppler]

Updates requested by @TaniaSchlatter above delivered. Built to test server.

[TaniaSchlatter]

Looks good. I think this is all set.

[TaniaSchlatter]

Looks good!