[15.0][FIX] project_timeline: Allow to install this module with project_enterprise

[alan196]

This PR fixes an issue added in commit https://github.com/OCA/project/commit/3689f1dfccf755c5d862c0e779ab0364215dea3a

When the module project_timeline is installed in a database with the module project_enterprise, it raises the following error:

psycopg2.errors.DuplicateColumn: column "planned_date_end" specified more than once

This is because the field planned_date_end is defined in both modules.

This PR checks if the field is already defined in the query before adding it.

Fixes https://github.com/OCA/project/issues/1433

[alan196]

@HugoCLU @carlos-lopez-tecnativa Could you help me to review 🙏

[pedrobaeza]

No, that was not what I requested. What I requested is that you make the if sentence more explicit, including quotes, comma or something, to make it match only when the exact column name is found, not in other case.

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[AaronHForgeFlow]

Superseded in https://github.com/OCA/project/pull/1564