Bump main branch version post 1.2 branch

[ElePT]

Summary

Preparing main branch for 1.3 development after creating the stable branch for the 1.2 series. This commit bumps all the version strings from 1.2.0 to 1.3.0 (and the backport branch for mergify to stable/1.2).

Details and comments

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Eric-Arellano
• @javabster
• @Qiskit/terra-core
• @kevinhartman
• @mtreinish

[coveralls]

Pull Request Test Coverage Report for Build 10096949789

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 9 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.008%) to 89.939%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	3	92.62%
crates/qasm2/src/parse.rs	6	97.61%

Totals
Change from base Build 10092758093:	-0.008%
Covered Lines:	66065
Relevant Lines:	73455

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💛 - Coveralls