feat: add --next-phase command to poetry version

[nfnvsc]

Pull Request Check List

Resolves: #1959

• Added tests for changed code.
• Updated documentation for changed code.

This PR include a new flag --next-phase for the poetry version command, which will only have impact when using the prerelease argument.

The behaviour of --next-phase is to increment the phase of the current version eg:

Current Version	Command	Updated Version
1.2.3a0	poetry version prerelease --next-phase	1.2.3b0
1.2.3b0	poetry version prerelease	1.2.3b1
1.2.3b1	poetry version prerelease --next-phase	1.2.3rc0
1.2.3rc0	poetry version prerelease	1.2.3rc1
1.2.3rc1	poetry version prerelease --next-phase	1.2.3

From my perspective this is the most correct way to handle the phases of the prereleases as defined by poetry-core version module.

[radoering]

Since there has been only positive feedback in #1959 so far, I think we can proceed.

The PR looks good in general, I just like to have another test that passes the command line parameter.

[nfnvsc]

Aligned the documentation table and added a new test with the command line parameter as requested @radoering

[github-actions]

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