What is the IUPAC Name of [Cr(NH3)5Cl]Cl2.NH3?
This answer is similar to this answer on $\ce{[Co(NH3)5(H2O)]Cl3}$, Thanks to Loong (Faded Giant) for the references.
According to the current version of Nomenclature of Inorganic Chemistry – IUPAC Recommendations 2005 (Red Book), the systematic names of coordination entities are generated by using the following principles:

IR-9.2.2.1 Sequences of ligands and central atoms within names
The following general rules are used when naming coordination compounds:
(i) ligand names are listed before the name(s) of the central atom(s),
(ii) no spaces are left between parts of the name that refer to the same coordination entity,
(iii) ligand names are listed in alphabetical order (multiplicative prefixes indicating the number of ligands are not considered in determining that order),
(…)

Therefore the systematic name of the co-ordination entity $\ce{[Co(NH3)5Cl]}$ would be &quot;pentaamminechlorido&quot; since the ammine ligands are named before the chlorido ligands according to alphabetical order.
The ionic composition of the complex salt $\ce{[Co(NH3)5Cl]Cl2}$ may be indicated in several ways:

IR-9.2.2.4 Charge numbers, oxidation numbers and ionic proportions
The following methods can be used to assist in describing the composition of a compound:
(i) The oxidation number of the central atom in a coordination entity may be indicated by a Roman numeral appended in parentheses to the central atom name (including the ending ‘ate’, if applicable), but only if the oxidation state can be defined without ambiguity. When necessary a negative sign is placed before the number. Arabic zero indicates the oxidation number zero.
(ii) Alternatively, the charge on a coordination entity may be indicated. The net charge is written in arabic numbers, with the number preceding the charge sign, and enclosed in parentheses. It follows the name of the central atom (including the ending ‘ate’, if applicable) without the intervention of a space.
(iii) The proportions of ionic entities in a coordination compound may be given by using
multiplicative prefixes. (See Section IR-5.4.2.1.)

According to the above rules, the oxidation state of cobalt in the complex can be written in two ways - as (III) or (3+).
Similarly the chloride ions can be named in two different ways - chloride or dichloride.
Also, see:

IR-5.5 NAMES OF (FORMAL) ADDITION COMPOUNDS
[...]
The names of the individual components of such a generalized addition compound are each constructed by using an appropriate nomenclature system, whether compositional, substitutive or additive. The overall name of the compound is then formed by connecting the names of the components by ‘em’ dashes; the proportions of the components are indicated after the name by a stoichiometric descriptor consisting of arabic numerals separated by a solidus or solidi. The descriptor, in parentheses, is separated from the compound name by a space. The order of names of the individual components is, firstly, according to the increasing number of the components and, secondly, alphabetical. As the only exception, the component name ‘water’ is always cited last. (Note that this represents a change from the rule in Ref. 2 according to which the component names must follow the order given by the formula.) The numerals in the descriptor appear in the same order as the corresponding component names.
[...]

$\ce{CaCl2.8NH3} \equiv \quad$  calcium chloride—ammonia (1/8)


Therefore the systematic names for the compound $\ce{[Co(NH3)5Cl]Cl2.NH3}$ would be:

pentaamminechloridocobalt(III) chloride—ammonia (1/1)
pentaamminechloridocobalt(3+) chloride—ammonia (1/1)
pentaamminechloridocobalt(III) dichloride—ammonia (1/1)
pentaamminechloridocobalt(3+) dichloride—ammonia (1/1)