Support for RPM spec files

Hi,

i think it will be a great feature if dependabot could support RPM's spec file.
There are a lot of projects and organizations that keep RPM sources on github, and they can easily benefit from dependabot
Parsing spec file's entries
`Name:`
'Version:'
'Patch*:'
'BuildRequires:'

for name's version, patches (official CVE), versioned buildrequires.

No source file, test, or entry point is named. Start by locating the existing Dependabot file parsers and their tests, then determine how RPM spec fields such as Name, Version, Patch*, and BuildRequires would map to dependency updates. Done means RPM spec files are parsed and supported update behavior is covered by tests.

Written by the indexing model from the issue text.