[WIP]Fix column type and validation for long webhook URL

[int128]

This fixes #1951.

Before submitting a pull-request to GitBucket I have first:

• read the contribution guidelines
• rebased my branch over master
• verified that project is compiling
• verified that tests are passing
• squashed my commits as appropriate (keep several commits if it is relevant to understand the PR)
• marked as closed using commit message all issue ID that this PR should correct

[int128]

I will check that MySQL, PostgreSQL and H2 supports column change to TEXT from VARCHAR. Please merge after that.

[int128]

Oops. It needs an index for TEXT column but it is not supported. Any ideas?
A webhook URL should be longer than 255 and cannot be VARCHAR.

[takezoe]

I have two ideas:

• Modify (or remove) constraints and keep consistency by application layer
• Add alternative columns which store hash value of text columns, and use these columns for constraints

I think the second one is a right way but it needs complex migration.

[ms502040]

I exactly dont'n know about H2 and pgsql, but mysql max varchar is 65,535 and max row length 65,535 bytes too The CHAR and VARCHAR Types, Row Size Limits:
H2 Limits and Limitations

There is no limit for the following entities, except the memory and storage capacity: maximum identifier length (table name, column name, and so on); maximum number of tables, columns, indexes, triggers, and other database objects; maximum statement length, number of parameters per statement, tables per statement, expressions in order by, group by, having, and so on; maximum rows per query; maximum columns per table, columns per index, indexes per table, lob columns per table, and so on; maximum row length, index row length, select row length; maximum length of a varchar column, decimal column, literal in a statement.

pgsql Character Types:

In any case, the longest possible character string that can be stored is about 1 GB

There is problem with max key length (in mysql 1024bytes, i think), but why indexing URL column? maybe you have reason for unique url per repository? (except noob users :) ) maybe better only index USER_NAME + REPOSITORY_NAME for webhook search when run it? little index = fast search
edit
for foreign key constraints to WEB_HOOK_EVENT set id (autoincrement, bigint) and use join for select