[BUGFIX] Limit primary key length on be_session and fe_session table

Patch for issue #79566 increased the field length of ses_name in
fe_session and be_session table from 32 to 255.
This field is used together with ses_id as primary key.
With utf8, this now exceeds maximum key length of 757 bytes.
To fix the issue, ses_name is cut down to 100 for the time being,
the patch should be fine for master and 7.6 this way.

Change-Id: I06abecca0f8df483590cf0a3c193134083e8f5f1
Resolves: #79628
Related: #79566
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/51538


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>