Extend length of PURL and PURLCOORDINATES columns from 255 to 786

[nscuro]

Description

Extends length of PURL and PURLCOORDINATES columns from 255 to 786.

Because PURLs are also used to populate the TARGET column of COMPONENTANALYSISCACHE, that column's length also has to be extended.

Addressed Issue

Fixes #2076

Additional Details

The length of 786 was chosen as a middle ground between the current 255 and the more optimal 1024. Mainly because MSSQL versions before 2016 have a maximum index key length of 900 (#2076 (comment)).

We don't want to break anything in that respect at the moment, and 786 should still be plenty of space.

Running DT with MySQL already takes manual effort, due to MySQL's even more restrictive key length limits (#271 (comment)). We're not making it worse by increasing the column length even more.

Tested upgrade from DT v4.10.1 to v4.11.0-SNAPSHOT for:

• H2
• MSSQL
• PostgreSQL

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have added corresponding update logic
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[codacy-production]

Coverage summary from Codacy

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Coverage variation	Diff coverage
✅ -0.10% (target: -1.00%)	❌ 0.00% (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (5a496b6)	21545	15971	74.13%
Head commit (72121d6)	21573 (+28)	15971 (+0)	74.03% (-0.10%)

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Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3560)	30	0	0.00%

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