[candidate] Allow dob format Y-m

[CamilleBeau]

Brief summary of changes

When a dob Format of Ym (year and month without day) is set in the config module, candidates could not be created for 2 reasons.

1. The wrong format (!Y-m-d) was being passed through the function DateTime::createFromFormat in the createNew function of the candidate class, which gave a wrong format error to the user even if they were passing through the expected format of Year-month
2. Even if this was fixed, the date was inserted into the candidate table as YYYY-MM, but this is not compatible with the SQL Type date

This PR fixes this issue by getting the date format from config, processing it to the right format and passing it through to DateTime::createFromFormat, as well as adding a '-01' to the end of the date if Ym format is selected in the configuration. This inserts the first of the month as the arbitrary date for a candidate.

• Have you updated related documentation?

Would someone be able to help me out as to whether this should be added to the changelog? I'm not sure if this is a bug introduced in 25 but I would be surprised if it existed in previous versions since it is so critical.

Testing instructions (if applicable)

1. Attempt to create a candidate with both 'Ymd' and 'Ym' selected as dob format in the configuration module.

Link(s) to related issue(s)

• Resolves Unable to create candidate because the date field doesn't allow inclusion of day of the month #8586

[racostas]

It is working.
Have some components of hack.
Not sure what will be doing in the case we have to show at some point this DoB and we override the day to the first of each month.
I don't see any other "easy solution"
I'm approving it.
I let the final judge to @driusan

[driusan]

For display, we can update any places that display it to honour the config if they're missing.

But I'm not sure if it should be the first or middle (15th) of the month, I think different projects use different days. Added something to the LORIS agenda to discuss/decide.