Set version number to 2.0.0rc1 for first release candidate (Qiskit#13953)

For the 2.0.0 release we're going to push release candidates prior to
the final to enable testing before we tag the final release. In
preparation for tagging the first release candidate this commit updates
the version string to indicate it's a release candidate. This commit
should be the final commit on main for 2.0.0rc1 and what gets tagged as
2.0.0rc1 post-merge. This will trigger the branch creation for
stable/2.0 which is where 2.0.0 will be tagged from.

Author: mtreinish

Cargo.lock

@@ -32,7 +32,7 @@
 # The short X.Y version
 version = "2.0"
 # The full version, including alpha/beta/rc tags
-release = "2.0.0"
+release = "2.0.0rc1"
 
 language = "en"
 

docs/conf.py

@@ -1 +1 @@
-2.0.0
+2.0.0rc1