Raise fixed token-length limit in hba.c.

Raise fixed token-length limit in hba.c.

Historically, hba.c limited tokens in the authentication configuration
files (pg_hba.conf and pg_ident.conf) to less than 256 bytes.  We have
seen a few reports of this limit causing problems; notably, for
moderately-complex LDAP configurations.  Increase the limit to 10240
bytes as a low-risk stop-gap solution.

In v13 and earlier, this also requires raising MAX_LINE, the limit
on overall line length.  I'm hesitant to make this code consume
too much stack space, so I only raised that to 20480 bytes.

Discussion: https://postgr.es/m/1588937.1690221208@sss.pgh.pa.us